rainfall infiltration and groundwater flow in a terraced slope of valtellina northern italy field data and modelling the aim of this work was to understand and reproduce the hydrological dynamics of a slope that is terraced by dry retaining walls this approach will help to assess the influence of temporary groundwater perched tables which can form at the area of contact between the backfill of the wall and the bedrock on the wall s stability the study area is located in valtellina northern italy near the village of tresenda which was affected by three debris flows that caused 18 casualties in 1983 in 2002 another event of the same type affected this area but that event only caused the interruption of a major transport road direct observations of one of the three flows in 1983 and the reconstruction of 2002 indicated that the most probable triggering cause was the collapse of a dry retaining wall after its backfill was saturated after field work was conducted to discover the principal hydrological and hydrogeological characteristics of the slope numerical modelling was performed to determine under what conditions the soil will saturate and therefore when the collapse of a dry retaining wall might occur first a study of the interaction between pluviometric events and groundwater behaviour was conducted then modelling was performed using finite element analysis software that permits the calculation of groundwater flow both for completely and partially saturated conditions the model was calibrated and validated using the hydrographs of the groundwater table recorded on site it can be used as a predictive instrument for rainfall events of a given duration and return period

esr dating of fault movement using various defect centres in quartz the case in the western south fossa magna japan the dates of movements of the itoigawa shizuoka tectonic line i s t l and minobu fault in the western south fossa magna have been obtained by esr dating measurements were made on various lattice defects of the ohc ge al and e centres in quartz grains of fault clay and quartz veins intruded at the time of movement all the dates obtained from these centres in quartz grains from two localities of the i s t l and iwo localities of the minobu fault fall in the range of 0 30 0 55 ma this suggests that all the centres were annihilated completely and that the obtained age can be admitted as the actual data of the latest fault movement meanwhile esr dates of quartz vein and fault clay in other localities locations 3 6 7 are divided into 0 30 0 55 ma and 1 5 2 0 ma which suggest incomplete resetting the dates of 0 30 0 55 and 1 5 2 0 ma might correspond to the clino unconformities observed in plio pleistocene sequence of this region

three dimensional spatial distribution of scatterers in galeras volcano colombia 1 a three dimensional spatial distribution of relative scattering coefficients is estimated for the galeras volcano colombia by an inversion of the coda wave envelopes from 1564 high quality seismic recordings at 31 stations of the galeras seismograph network the inversion reveals a highly non uniform distribution of relative scattering coefficients in the region for the two analyzed frequency bands 4 8 and 8 12 hz strong scatterers show frequency dependence which is interpreted in terms of the scale of the heterogeneities producing scattering two zones of strong scattering are detected the shallower one is located at a depth from 4 km to 8 km under the summit whereas the deeper one is imaged at a depth of 37 km from the earth s surface both zones may be associated with the magmatic plumbing system beneath galeras volcano the second strong scattering zone may be related to a deeper magma reservoir that feeds the system

10be and 26al evidence for exceptionally low rates of australian bedrock erosion and the likely existence of pre pleistocene landscapes analysis of in situ produced 10be and 26al demonstrate that some australian inselbergs granitic domes are among the most stable geomorphic surfaces in the world eroding at rates as low as 0 6 m myr twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0 5 myr and are eroding at a mean model rate less than 0 7 0 1 m myr n 6 isotopic analyses of samples collected from the top of mt wudinna little wudinna and yarwondutta rock are most consistent with continuous exposure during erosion on the other hand samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure these unique isotopic data provide the first quantitative information for evaluating longstanding but previously untested hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some eyre peninsula inselbergs are probably relict features of pre pleistocene landscapes

dating loess up to 800 ka by thermoluminescence thermoluminescence tl ages agreeing with expected ages have been obtained for 13 loess samples spanning the age range from 20 to 800 ka our samples are from alaska and north island new zealand and are unusual in tl dating studies of loess older than 80 100 ka by having independent age assignments that are generally well constrained from ages of associated tephra beds with the polymineral fine silt sized 4 11 m grains the partial bleach tl technique yielded expected ages up to about 350 ka whereas the total bleach method gave accurate ages in the range 100 to 800 ka thus the much disputed upper age limit of 100 150 ka for the tl dating of loess now appears to be sample and worker dependent rather than a global property of the tl signals in the tl dominant feldspars

representative rainfall thresholds for landslides in the nepal himalaya measuring some 2400 km in length the himalaya accommodate millions of people in northern india and pakistan nepal bhutan and parts of other asian nations every year especially during monsoon rains landslides and related natural events in these mountains cause tremendous damage to lives property infrastructure and environment in the context of the himalaya however the rainfall thresholds for landslide initiation are not well understood this paper describes regional aspects of rainfall thresholds for landslides in the himalaya some 677 landslides occurring from 1951 to 2006 were studied to analyze rainfall thresholds out of the 677 landslides however only 193 associated with rainfall data were analyzed to yield a threshold relationship between rainfall intensity rainfall duration and landslide initiation the threshold relationship fitted to the lower boundary of the field defined by landslide triggering rainfall events is i 73 90d 0 79 i rainfall intensity in mm h 1 and d duration in hours revealing that when the daily precipitation exceeds 144 mm the risk of landslides on himalayan mountain slopes is high normalized rainfall intensity duration relationships and landslide initiation thresholds were established from the data after normalizing rainfall intensity data with respect to mean annual precipitation map as an index in which ni 1 10d 0 59 ni normalized intensity in h 1 finally the role of antecedent rainfall in causing landslides was also investigated by considering daily rainfall during failure and the cumulative rainfall to discover at what point antecedent rainfall plays an important role in himalayan landslide processes rainfall thresholds presented in this paper are generalized so they can be used in landslide warning systems in the nepal himalaya 2008 elsevier b v all rights reserved

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

evidence suggesting that methods of rock varnish cation ratio dating are neither comparable nor consistently reliable abstract using samples from a prehistoric quarry site in the mojave desert we tested and compared the two principal methods of rock varnish cation ratio dating analysis of rock varnish scrapings r i dorn 1983 quaternary research 20 49 73 and 1989 physical geography 13 559 596 and analysis of rock varnish in situ c d harrington and j w whitney 1987 geology 15 967 970 because we found no consistent relationship between the varnish cation ratio k ca ti and the relative age of the varnish neither method could be used to cation ratio date the underlying chert artifacts moreover in situ analyses yielded systematically higher cation ratios and lower ti abundances than bulk analyses of scraped varnish or microprobe analyses of varnish in cross section our results when considered along with other recently published evidence indicate that these two methods of varnish chemical analysis and cation ratio dating may not be comparable nor consistently reliable chronometers

exposure dating and validation of periglacial weathering limits northwest scotland periglacial weathering limits on two mountains in northwest scotland separate zones of contrasting exposure history exposure dating of bedrock below the weathering limits gives ages consistent with late devensian deglaciation but six out of seven samples from above the weathering limits give minimum exposure ages older than late devensian ice expansion these results suggest that mountain summits stood as nunataks above the last ice sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation trimming of frost debris during an ice sheet readvance or enhanced weathering prior to climatic warming during ice sheet downwastage the dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold based ice on mountain summits and erosive warm based ice at lower elevations although 26 al 10 be ratios for high level bedrock surfaces provide no evidence of prolonged static ice cover

intrinsic and scattering attenuation in western india from aftershocks of the 26 january 2001 kachchh earthquake abstract 176 vertical component short period observations from aftershocks of the mw 7 7 26 january 2001 kachchh earthquake are used to estimate seismic wave attenuation in western india using uniform and two layer models the magnitudes mw of the earthquakes are less than 4 5 with depths less than 46 km and hypocentral distances up to 110 km the studied frequencies are between 1 and 30 hz two seismic wave attenuation factors intrinsic absorption qi 1 and scattering attenuation qs 1 are estimated using the multiple lapse time window method which compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model we first assume spatial uniformity of qi 1 qs 1 and s wave velocity a second approach extends the multiple scattering hypothesis to media consisting of several layers characterized by vertically varying scattering coefficient g intrinsic absorption strength h density of the media and shear wave velocity structure the predicted coda envelopes are computed using monte carlo simulation results show that under the assumption of spatial uniformity scattering attenuation is greater than intrinsic absorption only for the lowest frequency band 1 to 2 hz whereas intrinsic absorption is predominant in the attenuation process at higher frequencies 2 to 30 hz the values of q obtained range from qt 118 qi 246 and qs 227 at 1 5 hz to qt 4000 qi 4600 and qs 33 300 at 28 hz center frequencies being qt 1 a measure of total attenuation results also show that qi 1 qs 1 and qt 1 decrease proportional to f two rates of decay are clearly observed for the low 1 to 6 hz and high 6 to 30 hz frequency ranges values of are estimated as 2 07 0 05 and 0 44 0 09 for total attenuation 1 52 0 21 and 0 48 0 09 for intrinsic absorption and 3 63 0 07 and 0 06 0 08 for scattering attenuation for the low and high frequency ranges respectively despite the lower resolution in deriving the attenuation parameters for a two layered crust we find that scattering attenuation is comparable to or smaller than the intrinsic absorption in the crust whereas intrinsic absorption dominates in the mantle also for a crustal layer of thickness 42 km intrinsic absorption and scattering estimates in the crust are lower and greater than those of the mantle respectively

comparative analysis of contributing parameters for rainfall triggered landslides in the lesser himalaya of nepal in the himalaya people live in widely spread settlements and suffer more from landslides than from any other type of natural disaster the intense summer monsoons are the main factor in triggering landslides however the relations between landslides and slope hydrology have not been a focal topic in himalayan landslide research this paper deals with the contributing parameters for the rainfall triggered landslides which occurred during an extreme monsoon rainfall event on 23 july 2002 in the south western hills of kathmandu valley in the lesser himalaya nepal parameters such as bedrock geology geomorphology geotechnical properties of soil and clay mineralogy are described in this paper landslide modeling was performed in seep w and slope w to understand the relationship of pore water pressure variations in soil layers and to determine the spatial variation of landslide occurrence soil characteristics low angle of internal friction of fines in soil medium range of soil permeability presence of clay minerals in soil bedrock hydrogeology and human intervention were found to be the main contributing parameters for slope failures in the region

radiocarbon dating of soil organic matter radiocarbon ages of soil organic matter are evaluated with a model which incorporates the dynamics of the14c content of soil organic matter measured14c ages of soil organic matter or its fractions are always younger than the true ages of soils due to continuous input of organic matter into soils differences in soil c dynamics due to climate or soil depth will result in significantly different14c signatures of soil organic matter for soils of the same age as a result the deviation of the measured14c age from the true age of soil formation could differ significantly among different soils or soil horizons our model calculations also suggest that14c ages of soil organic matter will eventually reach a steady state provided that no climatic or ecological perturbations occur once a soil or a soil horizon has reached a steady state 14c dating of soil organic matter will provide no useful information regarding the age of the soil however for soils in which steady state has not been reached it is possible to estimate the age of soil formation by modeling the measured14c contents of soil organic matter radiocarbon dating of buried soils could in general overestimate the true age of the burial by as much as the steady state age of the soil or soil horizon

factors affecting 14c ages of lacustrine carbonates timing and duration of the last highstand lake in the lahontan basin abstract two processes contribute to inaccurate 14c age estimates of carbonates precipitated within the lahontan basin nevadacalifornia low initial 14c c ratios in lake water reservoir effect and addition of modern carbon to calcium carbonate after its precipitation the mast reliable set of 14c ages on carbonates from elevations 1310 m in the pyramid and walker lake subbasins indicate that lakes in all seven lahontan subbasins coalesced 14 200 14c yr b p forming lake lahontan lake lahontan achieved its 1330 m highstand elevation by 13 800 14 c yr b p and receded to 1310 m by 13 700 14c yr b p calculations based on measured carbonate accumulation rates of the amount of time lake lahontan exceeded 1310 and 1330 m 500 and 50 yr are consistent with this chronology the timing of the lake lahontan highstand is of interest because of the linkage of highstand climates with proximity to the polar jet stream the brevity of the lahontan highstand is interpreted to indicate that the core of the southern branch of the polar jet stream remained only briefly over the lahontan basin

40ar 39ar dating of latest pleistocene 41 ka marine tephra in the mediterranean sea implications for global climate records abstract fifty one 40 ar 39 ar laser heating analyses of sanidine crystals in the c 13 tephra layer recovered out of a piston core raised from 3000 m depth in the tyrrhenian sea yielded apparent ages between 25 and 112 ka twenty four of these measurements define an age probability maximum and generate an isochron of 41 1 2 1 ka 2 with a 40 ar 36 ar intercept of 288 21 that is indistinguishable from the modern atmosphere however the entire population is skewed toward older apparent ages with smaller peaks at 48 ka 55 ka 67 ka and 110 ka the composition of glass shards in the c 13 tephra overlaps that of the sio 2 rich phase of the 150 km 3 campanian ignimbrite which erupted from the campi flegrei caldera 130 km northwest of the core site although the 41 1 2 1 ka isochron is 15 older than k ar and 14 c ages for the campanian ignimbrite it is indistinguishable from recent 40 ar 39 ar age determinations the campanian ignimbrite eruptions were also chemically similar to and correlated with the y 5 ash layer the most voluminous and widely dispersed late pleistocene tephra in the mediterranean region the age of the y 5 layer was constrained originally at 38 0 2 5 ka on the basis of astronomical dating of o isotope stages the 40 ar 39 ar ages astronomical dating plus chemical similarities permit correlation of the c 13 tephra layer with both the campanian ignimbrite and the y 5 tephra layer the older ages preserved in the c 13 tephra layer may reflect xenocrysts incorporated during the explosive eruption accompanying collapse of the campi flegrei caldera 41 ka the c 13 tephra layer is correlated with a 10 be peak in an adjacent marine core o isotope stage 3 12 and immediately preceded a cooling episode corresponding to heinrich event 4 thus the age of these features is constrained by radioisotope dating the 41 ka peak in 10 be deposition is a global phenomenon whose age matches that of the laschamp geomagnetic excursion thus our results provide a new tie point among several polar ice core and marine proxy records of paleoclimate during the past 50 kyr precise age information independent of radiocarbon dating can be recovered from latest pleistocene marine tephra using the 40 ar 39 ar laser heating method despite the presence of multiple components that may have been incorporated during or after its deposition

seismic attenuation in a nonvolcanic swarm region beneath wakayama southwest japan 1 seismic attenuation in the wakayama swarm area of southwest japan is estimated by optimally fitting the theoretical s coda model to an average s coda envelope in the frequency range of 1 48 hz the average s coda envelope is confirmed to have a common decay curve independent of the source station distance intrinsic attenuation is found to peak at around 4 hz suggesting thermal diffusion in grain size or crack length domains with dimensions of the order of 0 7 1 mm which is reasonable for crustal rock scattering attenuation is well approximated by the relation 0 054f 1 in this frequency range with an inferred peak at 0 5 hz suggesting that the statistical model is characterized by an exponential autocorrelation function with a correlation length of about 1 km and a fractional velocity fluctuation of 21 scattering is the dominant cause of attenuation at frequencies below 2 hz while intrinsic attenuation becomes predominant above 4 hz although values of coda attenuation qc 1 generally lie between the total and intrinsic attenuation the differences between these three values becomes very small above 4 hz indicating that the coda attenuation measurements provide a reasonably good estimate of the total attenuation the total attenuation was found to coincide well with the total apparent attenuation estimated by a linear inversion using direct s waves from swarm earthquakes confirming the validity of the present results

206pb 230th 234u 238u and 207pb 235u geochronology of quaternary opal yucca mountain nevada abstract u th pb isotopic systems have been studied in submillimeter thick outermost layers of quaternary opal occurring in calcite silica fracture and cavity coatings within tertiary tuffs at yucca mountain nevada usa these coatings preserve a record of paleohydrologic conditions at this site which is being evaluated as a potential high level nuclear waste repository the opal precipitated from groundwater is variably enriched in 234u measured 234u 238u activity ratio 1 124 6 179 and has high u 30 313 ppm low th 0 008 3 7 ppm and low common pb concentrations measured 206pb 204pb up to 11 370 it has been demonstrated that the laboratory acid treatment used in this study to clean sample surfaces and to remove adherent calcite did not disturb u th pb isotopic systems in opal the opal ages calculated from 206pb 238u and 207pb 235u ratios display strong reverse discordance because of excess radiogenic 206pb derived from the elevated initial 234u the data are best interpreted using projections of a new four dimensional concordia diagram defined by 206pb 238u 207pb 235u 234u 238uactivity and 230th 238uactivity ages and initial 234u 238u activity ratios have been calculated using different projections of this diagram and tested for concordance the data are discordant that is observed 207pb 235u ages of 170 32 2 to 1772 40 ka are systematically older than 230th u ages of 34 1 0 6 to 452 32 ka the age discordance is not a result of migration of uranium and its decay products under the open system conditions but a consequence of noninstantaneous growth of opal combined u pb and 230th u ages support the model of slow mineral deposition at the rates of millimeters per million years resulting in layering on a scale too fine for mechanical sampling in this case u pb ages provide more accurate estimates of the average age for mixed multiage samples than 230th u ages because ages based on shorter lived isotopes are nonlinearly biased by younger mineral additions use of the combined u th pb technique to date yucca mountain quaternary opals significantly extends the age range beyond that of the 230th u dating method and shows that selected fracture pathways in the unsaturated zone felsic tuffs of yucca mountain have been active throughout the quaternary

stratigraphy and chronology of the galeras volcanic complex colombia copyright c 1997 elsevier science b v all rights reserved an understanding of the evolution of the galeras volcanic complex gvc is critical for assessing and refining hazards and eruption forecasting for the current reactivation of galeras volcano detailed field geology and dating by 14 c and 40 ar 39 ar methods help establish a comprehensive stratigraphic framework defining six different stages in the evolution of the galeras volcanic complex the two oldest stages cariaco and pamba represent the westernmost activity of the complex the next stage coba negra had a caldera forming eruption that occurred about 560 ka ago the coba negra edifice which was partially destroyed by this eruption had a total volume of about 70 km 3 the volume of pyroclastic flow deposits related to caldera formation is about 16 km 3 the caldera which has been partially destroyed was about 5 km in diameter the next constructional stage jenoy had an edifice volume of about 64 km 3 the caldera forming event that ended this stage took place sometime between 150 and 40 ka ago deposits from these eruptions are found in the northeastern and southeastern slopes of the complex and have a volume of approximately 2 km 3 the center of the jenoy caldera was located east southeast from the center of the previous coba negra caldera probably along the rim of the former caldera the diameter of the jenoy caldera was about 4 km a summit collapse probably not eruption related occurred between 12 and 5 ka ago during the urcunina stage hydrothermally altered rocks which are found in the scar of the collapse suggest that it may have been related to instabilities created by the circulation of hydrothermal fluids in addition to a very steep slope in the western part of the edifice the approximately 4 km 3 missing from the top of the volcano agrees very well with approximately 3 km 3 of avalanche deposits found near the town of consaca 12 km west of the present day summit the system at the gvc has produced large hazardous eruptions although in the most recent years less than 5 ka the eruptions have been of small scale

separation of intrinsic and scattering seismic wave attenuation in northeast india summary we have analysed the local earthquakes 2 0 ml 5 5 occurred in northeast ne india recorded by a temporary seismic network of 10 stations operated by national geophysical research institute ngri hyderabad to evaluate the relative contributions of scattering loss q 1 and intrinsic absorption q 1 to total attenuation q 1 using the multiple lapse time window analysis assuming multiple isotropic scattering in a medium of uniformly distributed scatterers the results show that q 1 is greater than q 1 at high frequencies f 3hz while the opposite is observed at low frequencies f 3hz the observed frequency dependence of q 1 corresponds to the scale length of lithospheric heterogeneity beneath ne india at least comparable with the wavelength for the lowest frequencies analysed of about 1km the observed q 1 for the study region obtained with single scattering theory is close to q 1 at high frequencies in agreement with theoretical prediction for an idealized case of uniform distribution of scatterers however a discrepancy exists between the two at low frequencies which can be explained by a depth dependent velocity and attenuation structure high value of q 1 is correlated with the geology and tectonic settings of the region characterized by himalayan and burman collision zones with a strong lateral heterogeneity the q 1 estimates obtained in this study can be used to infer the average temperature of the lower crust with an upper limit estimate of 800 c assuming a lower crustal gabbroic lithology

mechanical erosion and reheating of the lithosphere a numerical model for hotspot swells it is currently debated if either thermal erosion of the lithosphere or dynamical support is the source of topography and geoid anomalies the origin of tins controversy lies probably in the difficulty to model simultaneously these two effects for this purpose we have studied the time dependent behavior of two dimensional convection with a temperature and pressure dependent viscosity the use of a control volume method allows us to define a rigid zone simulating the mechanical lithosphere the interface between the lithosphere and the convective mantle is determined by a viscosity cutoff first some experiments model the rise of a plume below the lithosphere in order to observe the evolution of the uplift and thus to appreciate the various processes involved in the swell formation before the plume reaches the base of the thermal lithosphere an uplift a few hundred meters in amplitude develops which can only be ascribed to a pure dynamical support the major uplift occurs when the ductile part of the lithosphere the convective boundary layer is squeezed by the plume the reheating of the mechanical lithosphere takes place after this transient stage of dynamical erosion however this late process is very slow but can magnify the amplitude of the swell if the lithosphere stays long enough above the plume these results shed some light on the different mechanisms occurring during the swell formation but the configuration modeled does not correspond to the one expected for actual hotspot swells they feature plume rising up to the lithosphere while natural situations correspond to lithosphere drifting above preexisting plumes an experiment with a moving lithosphere was run and shows that thermal erosion does not affect significantly a moving lithosphere even for relatively slow drifting velocities few centimeters year indeed the thermal structure of the lithosphere is not modified above the 800 c isotherm except for a motionless plate in this case the resulting swell should be greater this could explain why azores crozet or cap verde swells are so high on the other hand the shape of a swell over a moving lithosphere is strikingly reminiscent of the hawaiian swell

analysis of multiple scattering at vesuvius volcano italy using data of the tomoves active seismic experiment data from the tomoves active seismic experiment are used to study scattering effects in the shallow heterogeneous structure of vesuvius volcano seismograms from shots located on the volcano itself are characterised by spindle like envelopes small or missing p onsets missing s onsets and long codas seismograms from shots in the surroundings of the volcano on the contrary show clear and impulsive p and s onsets and short codas the different shapes of the envelopes can be explained by strong multiple scattering in the shallow heterogeneous eruptive material of the volcano and single scattering in the surrounding crust the seismograms of shots located on the volcano are modeled using the diffusion model with a diffusivity of d 0 1 km2 s for the frequency range of 2 16 hz assuming the dominance of s waves in the coda and a typical s wave velocity of around 1 5 km s this corresponds to a transport mean free path ltr of only 200 m which is 3 orders of magnitude smaller than for normal earth crust these results show that multiple scattering is an important effect which cannot be neglected in the modeling of seismic wave propagation in volcanic environments

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

optical and radiocarbon dating at jinmium rock shelter in northern australia the jinmium rock shelter is located in the kimberley region of northern australia claims for ancient rock art and an early human presence at this site1 were based on thermoluminescence ages of 50 75 thousand years kyr for quartz sands associated with buried circular engravings pecked cupules and on thermoluminescence ages of 116 176 kyr for the underlying artefact bearing deposits here we report substantially younger optical ages for quartz sand and ages based on measurements of radioactive carbon in charcoal fragments from the occupation deposit using conventional multiple grain optical dating methods we estimate that the base of the deposit is 22 kyr however dating of individual grains shows that some have been buried more recently the single grain optical ages indicate that the jinmium deposit is younger than 10 kyr this result is in agreement with the late holocene ages obtained for the upper two thirds of the deposit from radiocarbon measurements we suggest that some grains have older optical ages because they receivedinsufficient exposure to sunlight before burial the presence of such grains in a sample will cause age overestimates using multiple grain methods whether using thermoluminescence or optical dating

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

controlling factors of loess landslides in western china based on detailed field data from recent geo hazards surveys in the loess plateau region of western china this study analyzes the key factors that control loess landslides the evolution phase of river valleys the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence distribution and other characteristics of loess landslides groundwater and vegetation also contribute to their formation a combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes

quaternary erosion and cosmic ray exposure history derived from 10be and 26al produced in situ an example from pajarito plateau valles caldera region 10 be and 26 al concentrations measured by accelerator mass spectrometry in 20 samples of quartz separated from rhyolitic volcanic ash flow tuffs collected on the pajarito plateau of the valles caldera new mexico were used to model time integrated erosion rates and cosmic ray exposure histories the model erosion rates determined for different stratigraphic units within the tshirege member upper bandelier tuff vary from 0 1 cm ka for the resistant unit to 1 1 cm ka for the softer unit intermediate erosion rates are thought to indicate earlier age cover by post tuff lithologies of different hardness the geographic distribution of these intermediate rates allows an approximate determination of the extent of material now gone stratigraphic ghosts periods of burial can be determined from 26 al 10 be ratios for the pajarito plateau burial most likely resulted from cover by soil and sediment held in place by vegetation our data allow us to model the duration and extent of thick forest cover which today exists only at higher altitudes

slow late paleozoic exhumation in the presidential range of new hampshire as determined by the 40ar 39ar relief method 40 ar 39 ar mineral ages from muscovite were used to determine exhumation rates in the multiply deformed and metamorphosed silurian and devonian metasedimentary rocks exposed on mount washington new hampshire the muscovite ages increase progressively from the bottom to the top of the mountain the oldest mount washington summit elevation 6200 ft 1900 m is 304 3 ma and the youngest route 16 elevation 1350 ft 410 ml is 274 3 ma the age and elevation data yield an exhumation rate of 0 04 mm yr the exhumation rate indicates that 1 the middle pennsylvanian through early permian was a period of very slow exhumation 2 rapid uplift associated with the acadian orogeny must have terminated by at least 305 ma 3 sometime after 274 ma renewed uplift created the present topography of the mount washington massif and 4 the relief method can be used successfully in older more deeply eroded orogenic belts if the topographic relief is adequate and cooling was slow

dating geomorphologic surfaces using cosmogenic 3he cosmogenically produced 3he in rocks can be used to date geomorphologic surfaces using the late pleistocene bonneville flood event the subsequent development of the provo shoreline and associated volcanic rocks a production rate of 432 atoms g yr in olivine is determined for 38 56 n latitude present geomagnetic latitude 46 5 at 1445 m altitude integrated over the last 14 400 years measurements of cosmogenic helium in flood deposits on river scoured surfaces and lava flows show that it is possible to date directly large scale events such as volcanic eruptions and catastrophic floods olivine and pyroxene are both satisfactory minerals for cosmogenic dating by the 3he method however in most cases plagioclase and quartz are unsuitable because they do not quantitatively retain helium isotopes in their lattices

response parameters for characterization of infiltration rainwater infiltration is of particular interest with respect to slope stability hazard management the process of rainfall infiltration into unsaturated soil is complex due to the number of soil parameters involved and the random nature of moisture flux boundary conditions in this paper the effect of rainfall intensity on infiltration is investigated through the use of finite element seepage modeling for a 5 m high soil column subjected to various rainfall intensities the numerical modeling study identified three response parameters that can be used to describe one dimensional infiltration into an unsaturated soil the response parameters are the depth of wetting front the matric suction reduction depth and the sectional infiltration rate the practical application of the rainfall response parameters in slope stability analysis is illustrated

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

s wave attenuation characteristics in the galeras volcanic complex south western colombia vertical component short period seismograms from 435 well located volcano tectonic earthquakes are used to estimate s wave attenuation in the galeras volcanic complex south western colombia using coda waves the coda magnitudes mc of the events are less than 2 event depths are less than 10 km and hypocentral distances up to 16 km intrinsic absorption q 1 i and scattering attenuation q 1 s are estimated by means of a fitting procedure between the observed and synthetic coda envelopes in four frequency bands 1 2 2 4 4 8 and 8 12 hz the observations are compared with the theoretical predictions by an accurate approximate analytical solution of the radiative transfer equation which is based on the assumptions of multiple isotropic scattering impulsive isotropic point source and a medium with homogeneous scattering and absorption properties results show that scattering is strong and it constitutes the predominant attenuation effect in this region in the frequency range analyzed in this study the values of the mean free path for scattering of s waves range between 2 7 l 8 1 km which are clearly higher than those obtained in other volcanic regions of the world but about two orders of magnitude smaller than average estimates for the earth s crust the characteristic length scale of intrinsic absorption gives values of 2 5 la 77 km which are on the same order as the usual values for the earth s crust 2010 elsevier b v all rights reserved

cosmogenic 36cl accumulation in unstable landforms 2 simulations and measurements on eroding moraines cosmogenic 36cl surface exposure ages obtained for multiple boulders from single landforms are usually characterized by a variance larger than that of the analytical methods employed this excessive boulder to boulder variability progressively more profound with increasing age of landforms is due to removal of soil and gradual exposure of boulders at the surface in our gradual exposure model boulders are initially buried in moraine matrix with time erosion lowers the moraine surface and the boulders are gradually exposed to cosmic rays because the cosmic ray intensity changes with depth the boulders are subjected to variable production rates of the cosmogenic 36cl initial depth of boulders and their chemical composition are variable which results in different amounts of the accumulated cosmogenic 36cl and thus different apparent ages of boulders the shape of the resulting distribution of the apparent ages and the coefficient of variation depend on the erosion depth while the first moment is a function of the true surface age and the erosion depth these properties of the apparent age distributions permit calculation of the surface age the erosion depth and also the average erosion rate we tested the model calculations using 26 boulders from a late pleistocene moraine at bishop creek sierra nevada california the set exhibited a bimodal distribution of the 36cl surface exposure ages we interpreted the older mode as the result of gradual exposure and the younger one as the result of surficial processes other than soil removal the 10 samples that constitute the older mode produced a distribution which closely matches the modeled distribution calculated using an age of 85 kyr and erosion depth of 570 g cm 2 this age is the same as an independent estimate obtained from cation ratio studies and the calculated erosion depth is very close to the erosion depth of 600 g cm 2 based on a simple analytical model of soil erosion these results indicate that our statistical model adequately describes effects of soil erosion on accumulation of cosmogenic 36cl the approach can be used to simultaneously obtain the true landform age and the erosion rate from apparent 36cl ages and thereifore may help in evaluation of surface exposure ages of eroding landforms

spatial distribution of scattering loss and intrinsic absorption of short period s waves in the lithosphere of japan on the basis of the multiple lapse time window analysis of hi net data summary propagation of short period s waves through the crust is strongly controlled by scattering loss and intrinsic absorption scattering loss controls the shape of the seismic envelope and the spatial distribution of the energy while intrinsic absorption produces an exponential decay as a function of time which is independent of the coordinates since both parameters have a different effect it is possible to compute them by means of the multiple lapse time window analysis mltwa in this paper high resolution maps of japan for both seismic s wave attenuation parameters are obtained by using the mltwa with data provided by the hi net seismic network the maps show strong regional variation of the parameters the variations depend mainly on the tectonic setting of each region and volcanism mechanisms in the scattering loss maps in the 1 2 hz map there is a very different behaviour between the northeast stronger scattering loss and the southwest much weaker scattering loss in the northeast of japan areas with strong scattering loss correspond mainly to the location of the volcanic arcs in southwest japan chugoku region and the west side of kii peninsula show strong scattering levels for the 4 8 hz and higher frequency bands in hokkaido strong scattering loss and intrinsic absorption can be observed for the lower frequency bands in the sendai plain we find strong scattering loss for all the frequency bands under all these areas low velocity anomalies have been detected in previous works in tohoku area the east side shows lower intrinsic attenuation than the west side this characteristic seems to extend to the southern part of hokkaido and to central japan in kanto area the values of intrinsic absorption are lower than in the surrounding areas but in the region around the itoigawa shizuoka tectonic line and in its western side strong absorption areas are observed the behaviour of each area for intrinsic absorption is similar to the behaviour observed in the q 1c maps the mltwa is based on the hypothesis of multiple isotropic scattering in a medium with the homogeneous distribution of scattering mean free path and intrinsic absorption although these hypotheses are very simple the results are very informative on the characteristics of each region and show the usefulness of studying the properties of scattered seismic waves in the understanding of the properties of the crust

monitored and simulated variations in matric suction during rainfall in a residual soil slope this research combines field laboratory and numerical investigations to estimate the development of a wetting front within a 1 2 m residual soil mantle on a steep forested slope during rainfall events the field monitored variations in matric suction due to rain water infiltration during various events revealed that the maximum infiltration rate was much higher when the wetting front resided in the upper 20 cm of soil compared to the case when the wetting front advanced to depths 20 cm laboratory investigations on soil hydraulic properties i e soil water characteristic curve and hydraulic conductivity were useful to establish the parameters of a multilayer finite element model for one dimensional vertical infiltration these parameters were subsequently calibrated by matching the predicted and field measured transient pore water pressure responses during actual rainstorms with irregular rainfall patterns the calibrated simulation model was used to assess the migration of the wetting front under uniform rainfall with different intensities based on the numerical results a hyperbolic equation was developed to predict the duration of uniform rainfall required for the propagation of wetting front to a certain depth for a given rainfall intensity the proposed equation was subsequently tested against field monitored advancements of the wetting front during real rainstorms with variable rainfall intensity

numerical modeling of rainstorm induced shallow landslides in saturated and unsaturated soils for the assessment of shallow landslides triggered by rainfall the physically based model coupling the infinite slope stability analysis with the hydrological modeling in nearly saturated soil has commonly been used due to its simplicity however in that model the rainfall infiltration in unsaturated soil could not be reliably simulated because a linear diffusion type richards equation rather than the complete richards equation was used in addition the effect of matric suction on the shear strength of soil was not actually considered therefore except the shallow landslide in saturated soil due to groundwater table rise the shallow landslide induced by the loss in unsaturated shear strength due to the dissipation of matric suction could not be reliably assessed in this study a physically based model capable of assessing shallow landslides in variably saturated soils is developed by adopting the complete richards equation with the effect of slope angle in the rainfall infiltration modeling and using the extended mohr coulomb failure criterion to describe the unsaturated shear strength in the soil failure modeling the influence of rainfall intensity and duration on shallow landslide is investigated using the developed model the result shows that the rainfall intensity and duration seem to have similar influence on shallow landslides respectively triggered by the increase of positive pore water pressure in saturated soil and induced by the dissipation of matric suction in unsaturated soil the rainfall duration threshold decreases with the increase in rainfall intensity but remains constant for large rainfall intensity

using strontium isotopes to determine the age and origin of gypsum and anhydrite beds the variation of 87sr 86sr in seawater with time can be used to determine the age of calcium sulfate beds precipitated from brine derived from seawater the determination of a marine origin can be established by the consistency of strontium isotope results from samples at different stratigraphic levels in a single gypsum anhydrite bed collected at separated sites the scatter of strontium isotope results in the gypsum anhydrite samples examined here is interpreted to result from the contribution of meteoric strontium to the salina strontium isotope results from three evaporite settings the jurassic todilto formation from new mexico the permian blaine formation from blaine county oklahoma and the permian salado formation from new mexico are used to determine the age and origin of the parent brine for these gypsum anhydrite beds the calcium sulfate beds from each of these formations precipitated from salinas that originated with a marine flooding but show at different times and localities volume do

ambiguities in direct dating of rock surfaces using radiocarbon measurements an attempt was made to date rock surfaces with accelerator mass spectrometry ams radiocarbon measurements of rock varnishes or rock weathering rinds in two case studies samples pretreated in the laboratory of dr ronald dorn prior to ams analysis have been found to contain significant quantities of carbon rich materials of two distinct classes type i material resembles bituminous coal whereas type ii material resembles pyrolized wood charcoal fragments in samples where these type i and type ii materials were separated and ams radiocarbon dated they were found to have widely differing radiocarbon ages in these cases the measurement of the radiocarbon age of the entire sample would yield results that are at best ambiguous neither type i nor type ii materials were found in comparable samples that were independently prepared

scattering behaviour at merapi volcano java revealed from an active seismic experiment summary the seismic structure of the stratovolcano merapi java indonesia was studied using an active seismic experiment three 3 km long seismic profiles each consisting of up to 30 three component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level the detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting the seismic experiment at merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome where the sources of most of the natural volcanic seismic events are located the cone of merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material additionally the topography of the erosion valleys leads to an irregular deposition which cannot be described by a simple 1 d layering these inhomogeneities have a strong influence on seismic signals the direct p and s waves are attenuated quickly and show only small amplitudes on seismograms the energy lost from the direct waves however is not changed into heat but scattered and can be observed as seismic coda following the direct waves the observed seismograms show a spindle like amplitude increase after the direct p phase this shape of the envelope can be explained by the diffusion model according to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves besides the envelope the coherence and polarization properties of the wavefield also indicate strong scattering only the first onset shows coherence over a station spacing of 100 m whereas the late phases carrying the major part of the energy are mainly incoherent the horizontal components of the seismograms have larger amplitudes than the vertical component but within the horizontal plane the polarization is almost arbitrary corresponding to waves arriving from scatterers located arbitrarily in space as a result of the inversion using the diffusion model we obtain values of the s wave scattering attenuation coefficient gs and the s wave intrinsic absorption coefficient gi in the frequency range of 4 20 hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption gs gi the mean free path of s waves is as low as 100 m gs1 100 m the scattering coefficient is independent of frequency gsyf 0 0 whereas the coefficient of intrinsic attenuation increases with increasing frequency giyf 1 6 the natural seismic signals at merapi volcano show similar characteristics to the artificial shots the first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves therefore these signals appear to be strongly affected by multiple scattering also

accuracy of rock varnish chemical analyses implications for cation ratio dating to compare methods of rock varnish chemical analysis and cation ratio determination we prepared three glass standards synthetic analogues of rock varnish analysis of these standards demonstrates that material of varnishlike composition can be accurately and precisely analyzed by means of quantitative energy dispersive electron microscopy sem eds however a blind interlaboratory comparison and reexamination of published data show that most published cation ratios of varnish are probably inaccurate because the technique used most frequently to determine rock varnish composition proton induced x ray emission pixe did not accurately measure the concentration of ti in the presence of ba a ubiquitous component of rock varnish this inaccuracy suggests that the premise of cation ratio dating and dates generated by this method should be reevaluated

relative and absolute dating of land surfaces abstract the dating of land surfaces has long posed problems for geomorphologists relative methods stratigraphic geomorphic topographic are sound and convincing exhumed forms may complicate identification and relationships for both epigene and etch forms have been buried and exhumed but in tectonically undisturbed areas the higher surfaces are older than those preserved at lower levels also surfaces have an age range the relationship of surfaces with volcanic deposits old shorelines and genetically related sedimentary sequences provides sound ages and correlation with dated duricrusts and faults is also useful there are no temporal limits to relative dating for the methods are equally applicable to the dating say of proterozoic surfaces as of those of pleistocene age the disadvantage of such methods is that the necessary evidence is frequently either not preserved or not exposed the so called absolute physical numerical methods and especially those based on exposure age dating with in situ cosmogenic radionuclides are appealing because they produce direct numerical ages and appear to be widely applicable but there are severe temporal limitations and sampling problems complicate and may invalidate interpretation absolute age determinations must be consistent with the stratigraphic and geomorphologic settings the best results are obtained when physicists and earth scientists pool their knowledge and experience a background in local and regional geology is especially important

radiative transfer and diffusion of waves in a layered medium new insight into coda q summary this paper is devoted to the study of the seismic coda in inhomogeneous media exhibiting a discontinuity of physical properties at a given depth we focus on the problem of a layer overlying a half space and analyse the precise effect of a contrast of wave velocities and or scattering strengths between them in order to model s codawave envelopes we solve the radiative transfer equation by the monte carlo method thereby neglecting the polarization i e the acoustic approximation we pay special attention to the transition towards the diffusion regime under the assumption of an almost isotropic intensity field a diffusion equation can be derived from the radiative transfer equation and we accurately determine the boundary conditions associated with our models analytical solutions of the diffusion equation have been obtained and systematically compared to the numerical solutions of the radiative transfer equation we identify the domain of validity of the diffusion approximation which provides a simple analytical form for the decay in the late coda we apply our theoretical investigations to the continental lithosphere if the scattering strengths of the mantle and the crust are assumed to be of the same order a velocity contrast at the moho will according to our theory amplify the coda signal since part of the energy is trapped in the crust an amplification factor is defined and given explicitly as a function of the reflection coefficients and the velocity contrast at the moho the shape of the long time decay is of the algebraic form f 3 2 like that of a uniform half space on the other hand if the scattering strength of the mantle is small with respect to that of the crust the decay in the diffusive regime is predicted to be of the form r i exp 2nft qa where q is a function of the reflection coefficients at the moho the mean free path of waves in the crust and frequencyf the coefficient q quantifies the rate at which the partially trapped energy leaks from the crust into the mantle this formula has the same form as that proposed by aki chouet 1975 to fit coda observations which has since been widely used to deduce the qc parameter with realistic model parameters we find that q roughly equals the parameter qc deduced from observations this shows that the effect of partial trapping of energy in the crust may be significant consequently seismic albedos of the crust may have been underestimated in previous studies in our theory the energy decay of seismic coda waves is determined by the layered structure of the earth that is a highly heterogeneous crust overlying a rather homogeneous mantle such structure is confirmed by geological and geochemical studies

cosmogenic 36cl dating of a young basaltic eruption complex lathrop wells nevada it has been proposed that the lathrop wells volcanic center a late quaternary basaltic complex in southern nevada has erupted more than once in common with most quaternary basalts this volcanic center has proved difficult to date by k ar and other commonly employed methods we have measured the accumulation of 36 cl in 11 samples from lava flows and volcanic bombs and obtained a combined average age of 81 7 9 ka with no systematic differences between sample subsets collected from different volcanic features the 36 cl dates do not support a history of multiple eruptions but neither do they completely preclude the possibility

an alluvial surface chronology based on cosmogenic36cl dating ajo mountains organ pipe cactus national monument southern arizona abstract a chronology of alluvial surfaces on piedmont slopes below the western ajo mountains southern arizona has been obtained using cosmogenic 36 cl accumulation and ams radiocarbon dating the apparent 36 cl ages of individual boulders range from 520 000 to 13 000 yr and the 14 c ages of organic material in the two young terraces are 2750 2350 and 17 800 cal yr b p the sequence of 36 cl ages is consistent with the apparent stratigraphic order but groupings of similar ages for different surfaces appear to result from repeated reworking of older surfaces associated with the deposition of younger ones the youngest surface gave a distribution of 36 cl ages about 30 000 yr older than the 14 c and soil ages however this distribution had 36 cl ages that overlapped with 36 cl ages from active channels and hillslopes we attribute the older than expected exposure ages of sampled boulders to inheritance of 36 cl while residing near the surface during very slow erosion on the mountain front our results show that although cosmogenic nuclide accumulation can help establish chronologies for surfaces in piedmont settings care must be used in evaluating the effects of complex exposure histories

unusual low frequency volcanic seismic events with slowly decaying coda waves observed at galeras and other volcanoes abstract events with slowly decaying coda waves are observed in active andesitic volcanoes associated mainly with vulcanian type eruptions or large gas emissions however these signals are also recorded in some quiescent volcanoes these unusual signals are considered to be related to magmatic activity and generally occur beneath the active crater the signals have been observed to be a short term precursor galeras volcano colombia 1992 1993 asama yama volcano japan 1983 after eruption tokachi dake volcano japan 1989 during seismic swarms meakan dake volcano japan 1982 and during quiescence puracevolcano colombia 1994 1995 tarumai volcano japan 1970 1971 1975 spectral analysis reveals common characteristics for this type of signal the spectrum is characterized by one or several sharp frequency peaks fundamental frequencies are not affected by epicentral distance azimuth or travel time indicating a source effect the damping coefficient for coda waves ranges from 0 002 to 0 02 and is related to large values of the quality factor q c ranging from 250 to 25 respectively these parameters may be the result of large amounts of gas bubbles in the magma body

cosmogenic 10be and 3he accumulation in pleistocene beach terraces in death valley california u s a implications for cosmic ray exposure dating of young surfaces in hot climates to investigate the history of pleistocene lake levels in the southwestern u s a and to improve our understanding of the systematics of in situ produced cosmogenic nuclide accumulation in hot climates and young rocks we examined the 3he 10be and 26al contents of quartz separates from metamorphic quartzites and quartz rich felsic rocks incorporated in a series of stranded conglomerate beach ridges ranging from 3 to 160 m above sea level in death valley california calculated 10be ages range from 17 to 135 kyr with most ages between 20 and 60 kyr in contrast cosmogenic 3he contents indicate exposure ages of 1 kyr except for one sample at 18 4 kyr for which the 10be age is still significantly greater 44 11 kyr 26al10be ratios close to the cosmogenic production ratio rule out the presence of meteoric 10be and point to 3he loss as the cause of the age discrepancies comparison to laboratory diffusive loss measurements using a diurnal direct solar heating model implies the 3he loss occurs because the effective quartz grain sizes are 100 m far smaller than the 1 3 mm fracture spacings estimated from thin sections because direct insolation enhances 3he loss sampling from shallow depths 20 40 cm may be useful in some cases 4he and 20ne measurements demonstrate that small amounts of radiogenic and atmospheric 3he are also present at levels equivalent to a few kiloyears sea level exposure which should be taken into account when dating surfaces of similar age the lack of any clear progression with terrace altitude and the occurrence of two fold variations in apparent exposure ages within individual terraces suggest that the 10be contents do not solely represent accumulation in the present sample locations instead accumulation probably also occurred during sample exposure in the higher altitude beach rock source regions and during fluvial transport to the ancient lake shore thus the beach terrace exposure ages of 20 60 kyr are probably maximum ages for the times of these high lake level stands in death valley

separation of intrinsic and scattering q for volcanic areas a comparison between etna and campi flegrei abstract we studied the seismic attenuation in the short period range 1 24 hz at the campi flegrei volcanic area using the method of frankel 1991 to separate intrinsic and scattering attenuation parameters the results compared to those obtained at etna volcano show that scattering phenomena play a main role in the attenuation mechanism of the seismic waves for these two volcanic areas the comparison of the present results with those obtained in non volcanic areas allow us to re consider the importance of the molten materials magma as a main cause of the seismic attenuation in the active volcanic areas

the use of duricrusts and topographic relationships in geomorphological correlation conclusions based in australian experience though there are many possible pitfalls duricrusted surfaces provide morphostratigraphic markers which are useful in preliminary extrapolation and correlation at the local and regional scales especially if other factors such as landscape evolution and topographic relationships are also considered particular reference is made to ferruginous and siliceous cappings close stratigraphic dating of the duricrusts allows regional differentiation but correlations are preferably intra rather than inter regional and are at best general and involve age ranges rather than narrow time frames problems broached include type of landscape development the relation of surface and duricrusts and the temporal equivalence of duricrust facies i e duricrusts of similar chemical tendencies but contrasted morphology the roles of duricrusts in relief inversion surface preservation and climatic interpretation are also mentioned

failure characteristics of rainfall induced shallow landslides in granitic terrains of shikoku island of japan soil slips debris slides and flow occurrences on hill slopes of particular areas are closely related to the mode of rainfall because of geological geomorphological and climatic settings japan is highly prone to rainfall induced landslides in 2004 shikoku the smallest island of japan faced extreme events of typhoon rainfalls and suffered huge losses of life and property because of floods and landslides this paper deals with the synoptic descriptions of failures that occurred in the granitic terrain of northeast shikoku island japan along with rainfall and failure relationships during the typhoon 0423 tokage of 2004 examples of typical failures that occurred in moriyuki and monnyu of northeast shikoku are taken into consideration in this study data from laboratory and field were used to perform sensitivity and stability analyses with respect to varying slope angles strength parameters and thicknesses of saturated residual soil this study attempts to employ a standard method of stability analysis of translational slides which are very common in masa soil weathered granite during extreme rainfall average rainfall intensities and duration during typhoon tokage were also used to interpret landslide triggering thresholds for the study area

residence time of diffuse waves in the crust as a physical interpretation of coda q application to seismograms recorded in mexico summary we consider a simple model for elastic wave propagation in the earth s litho sphere consisting of a heterogeneous and scattering crust overlying a homogeneous mantle that is we neglect backscattering from the upper mantle this rough condition is not strictly valid everywhere but this model allows us to investigate the effects of variations of diffracting properties between crust and mantle on the coda decay the free parameters describing the wave propagation are the mean free path of the waves and the intrinsic absorption in the crust in the framework of the radiative transfer theory we treat accurately jumps in s wave speed and the mean free path at the moho without intrinsic absorption this configuration yields a synthetic coda decay 1 texp 2 ft qc a form similar to that proposed by aki chouet 1975 to parametrize the observations the exponential decay in our purely elastic model is due to the partial leakage of diffuse energy into the mantle in order to test the applicability of our model we have determined the coda q parameter qc in the 1 15 hz frequency band from data recorded at four stations in mexico in the low frequency regime around 1 hz we suggest that the energy leakage significantly affects coda q whilst at higher frequencies around 10 hz the anelastic attenuation dominates a weak intrinsic absorption expressed by a frequency independent parameter qi of about 1000 accounts satisfactorily for the observed qc values in the whole frequency range our very simple model has only two free parameters and offers an attractive alternative physical interpretation of coda q in mexico this model is sufficient to interpret the coda observations according to our model in regions where the mean free path is much larger than the crustal thickness weakly heterogeneous crust the leakage effect should be small and the observed qc will mainly be due to the intrinsic absorption on the other hand when the mean free path is of the order of the crustal thickness strongly heterogeneous crust we predict a strong sensitivity of the decay rate of the coda to the crustal thickness this dependence may be important for the interpretation of the regional variations of coda q we propose introducing a new parameter d the residence time of diffuse energy in the crust which is physically more meaningful than a quality factor to quantify the leakage effect

separation of intrinsic and scattering attenuation using single event source in south korea abstract simultaneous use of numerous events in the multiple lapse time window analysis mltwa method is the most effective way to obtain and values such simultaneous use of numerous events normally shows a large observational scatter which may be caused by different radiation pattern and focal depth of each earthquake and regional alteration of the local structure to avoid these scattering factors the current study attempted to use single event source as the input data in mltwa for south korea the direct simulation monte carlo dsmc method was used to simulate the observations which showed realistic results when the number of recorded stations was eight or more the obtained values of seismic albedo b 0 were less than 0 5 which were in accordance with the same in the previous results three envelopes constructed by combination of three regional values of at 1 hz produced regional variations of which the ones at high frequencies of and at low frequencies of were remarkable this result showing the local variation indicated an advantage of the study using single source event over the previous studies in south korea that involved extensively distributed data because dsmc was known to be applicable to 3d structure due to its simple algorithm the current study also tried to correct radiation pattern of the observations by inserting focal mechanism algorithm to the code of the dsmc method such insertion however generated extremely low values of because the geometrically shrunk receiver could not capture most of the scattered particles this receiver problem is most likely to be a major obstacle of the 3d study of dsmc in addition the significant depth effect of q 1 was identified for the prior mltwa studies resulting from different measurement range and focal depth

comparative uranium thorium and thermoluminescence dating of weathered quaternary alluvium in the tropics of northern australia abstract thermoluminescence tl age determinations of alluvial sediments in the tropics are evaluated by comparison with u th age determinations of pedogenic accumulations in the alluvium of the lower gilbert river a large fan delta in the wet dry tropics of northern queensland australia this study extends u th dating by applying it not only to calcretes but also to fe mn oxyhydroxide oxide accumulations while a direct correlation cannot be made between u th dates from secondary minerals and tl dates from the host sediments both sets of data show broad consistency in addition to providing a minima for acceptable tl ages u th dates are useful for determining the chronology of pedogenesis diagenesis they show that calcretes and ferricretes have formed under similar climatic conditions in the wet dry tropics of northern australia during the late pleistocene beneath about 5 12 m the gilbert fan delta consists of an extensive sand body older than 85 000 yr and probably about 120 000 yr in age representative of a period of major fluvial activity not repeated since this time above are muds and fine sandy muds that extend uninterrupted to the present surface except in the downstream fan where they are bisected by a thin unit of medium sand that tl dates at 40 000 50 000 yr b p a system of sandy distributary channels over the fan surface represents an early holocene fluvial phase probably more active than at present

stable isotope geochronology of the australian regolith australian regolith profiles can be assigned to one of three post palaeozoic age groups on the basis of the oxygen isotope composition of authigenic clay minerals developed in the profile systematic variations in the isotopic composition of meteoric waters and therefore of the authigenic regolith minerals that formed in equilibrium with them are a result of the continent s drift from high to low latitudes and changes in global climate residual clays collected in situ from regolith profiles of post mid tertiary age have 18o values between 17 5 and 21 3 with the exception of samples from northern australia north of approximately 20 s which have anomalously low values because meteoric waters in northern australia are largely derived from monsoonal rain the high 18o values of post mid tertiary residual clays are consistent with australia s northward drift to low warm latitudes during this time compared with the much higher latitudes it occupied for most of its post palaeozoic history late tertiary residual clays have 18o values that are indistinguishable from all other post mid tertiary clays indicating that further subdivision of the sample groups is not feasible on a continent wide scale comparison with hypothetical modern clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in australia since the mid tertiary pre mid tertiary clays have lower 18o values between 10 0 and 17 5 which are consistently lower than post mid tertiary clays 18o values of less than 14 to 15 are thought to reflect weathering events during much earlier geologic periods perhaps early or mid mesozoic when australia was at high latitude and the australian climate was humid and cool to cold several workers have documented the existence of very old regolith profiles and land surfaces in australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre late mesozoic age which have 18o values between 10 2 and 12 3 regolith profiles composed of low 18o clays 15 are widespread in australia and it is possible that a much greater part of the modern landscape than previously recognized developed in the early or mid mesozoic the 18o values of transported i e sedimentary kaolinites reveals that the major source for many tertiary kaolinitic sediments was this postulated pre late mesozoic low 18o regolith the stableisotope evidence that much of the australian regolith formed in comparatively cold conditions suggests that contrary to some traditional interpretations lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub tropical climates the hydrogen isotope composition of the clays range from 115 to 50 however it is inferred that the majority of clays have undergone some post formational hydrogen isotope exchange which renders their d composition unsuitable for dating purposes

geomorphology of the gran sabana guayana shield southeastern venezuela abstract the forms of the gran sabana have been developed mainly on rocks of the gently folded precambrian roraima group a sequence of quartzites and siliceous conglomerates with intercalated jasper chert arkose siltstone and shale locally intruded by diabase dikes and sills two planation surfaces are preserved on the gran sabana the auyan tepui 2000 2900 m elevation and the wonken 900 1200 m surfaces with a speculative mesozoic initial age they are still extending table mountains dominate the landscape they comprise pediments foothills precipitous scarps hundreds of meters high a rim and a flattish summit the table mountain topography is controlled by joint systems water percolates along joints and bedding planes dissolves the siliceous cement the quartzite disaggregates and large blocks are isolated and collapse accumulating at the foot of the scarps and on top of the table mountain summits the percolating water forms large and intricate cave systems which frequently emerge in the scarp zone as high waterfalls these mark the lowest level of erosion of the table mountains karstic structures are prominent in the summit zone the evolution of the table mountain topography has been controlled by a combination of tectonic structural stratigraphic climatic and temporal factors

latest pleistocene lake shorelines and glacial chronology in the western basin and range province u s a insights from ams radiocarbon dating of rock varnish and paleoclimatic implications accelerator mass spectrometry radiocarbon dating of organic matter in the basal layer of rock varnish provides a minimum surface exposure age for the underlying landform varnishes 14c ages indicate that the latest pleistocene highstand of lake lahontan was abandoned before 12 7 ka searles lake before 13 6 ka lake manly before 13 0 ka and lake mojave before 11 6 ka the maxima of the tioga glaciation at pine creek in the eastern sierra nevada california and the middle creek glaciation in the adjacent white mountains of california nevada was just before 18 19 ka major recessional moraines were deposited in these ranges before 12 13 ka penecontemporaneous glacial retreat and high levels in closed basin lakes cannot be explained by glacial melt water but probably reflects higher snowlines and more precipitation a relatively minor glacial advance perhaps related to the younger dryas in europe may be penecontemporaneous with a slight transgression in lake levels about 10 11 ka in the western basin and range suggesting a temporary return to cooler or wetter conditions or both at the termination of the pleistocene

segmentation of alluvial fans in death valley california new insights from surface exposure dating and laboratory modelling laboratory experiments recent paleoenvironmental analyses of rock varnish and surface exposure dating of geomorphic units have led to new insights into the process of entrenchment and segmentation of alluvial fans and into the history of quaternary sedimentation in death valley entrenchment begins at the fanhead as the trench deepens its down slope end migrates down fan taking several tens of thousands of years to reach lower parts of the fan laboratory experiments suggest however that a new segment begins to grow at the toe long before the trench reaches this part of the fan furthermore the initial slope of the segment is not the equilibrium slope field evidence supports this model the tectonic tilting that caused entrenchment and segmentation in death valley may have been triggered by loading of the valley with water sedimentation on the salt pan in southern death valley is not at present in equilibrium with that on the fans rather it seems to be adjusting to an increase in the amount of fine material reaching the playa due in part to breaching of the outlet of lake tecopa somewhat after 600 ka bp and in part to subsidence of different parts of the valley at different rates failure to recognize this disequilibrium resulted in errors in earlier estimates of the age of the segmentation events

a warning system for rainfall induced shallow failures abstract it is widely recognised that soil slips and debris flows are triggered by short intense storms owing its geologic geomorphologic and climatic settings the piedmont region nw italy is highly prone to the occurrence of this kind of landslides in the last two centuries in fact a total of 105 severe meteoric events which triggered shallow failures occurred and of these 18 events took place from 1990 to 2002 a fair number of rainfall thresholds have been proposed in the literature defined both on empirical or on physical bases empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides while physical thresholds are based on numerical models that consider the relation between rainfall pore pressure and slope stability the main objective of this paper is the identification of the empirical triggering thresholds for the piedmont region four meteoric events were selected and analysed november 4 5 1994 july 7 8 1996 april 27 30 2000 october 13 16 2000 because they supply a wide range of variation for both rainfall parameters duration intensity cumulative rainfalls and the number of induced landslides in the intensity duration plot the critical limit is described by the equation i 19d 0 50 where i rainfall intensity expressed in mm h and d rainfall duration expressed in hours such a limit is traced to envelop 90 of the points on the graph in the ni d diagram the triggering thresholds are given by the equations ni 0 76d 0 33 and ni 4 62d 0 79 where ni normalised intensity with respect to the annual precipitation map expressed in mm h pma 100 in the article the different meaning of these thresholds is discussed finally the diagram ni ncr is proposed the triggering threshold is given by the expression ni 0 09ln ncr 0 54 where ncr is the normalised cumulative critical rainfall mm pma 100 the application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide prone areas is discussed in detail an operating procedure which is presently being verified and tested in the studied area is described

magnetic ages of some indian laterites abstract the results of an extensive palaeomagnetic investigation of laterites from peninsular india are described from 62 samples 693 specimens were step wise thermally demagnetised to eliminate secondary magnetisations the ages of laterite formation were estimated after calculation of pole positions from site mean directions and comparison with the mesozoic tertiary apparent polar wander path apwp for india the high altitude laterites have undergone a complex magnetic history during the late cretaceous and early tertiary the low altitude laterites are mid to late tertiary in age a fundamental mechanism in laterite formation and preservation is suggested when the indian laterite results are compared with those from australia they are seen to be consistent with the relative timing of the northward drift of india and australia

the hydrogeological attributes and mechanisms of a receding sedimentary terrain in the anambra basin southern nigeria this research investigated the hydrogeological aspects associated with severe gulling and landsliding on a vulnerable sedimentary terrain in the context of the newly identified deformation patterns and large numbers of recently discovered scars clustering slopes on identical coordinates results of field survey remote sensing vertical electrical sounding and experimental analyses were presented to explain the causes and mechanisms of the mass movements ravaging the terrain a digital elevation model accurately captured the diverse geomorphologic elements including landslide scars hills ridges valleys plains and rivers that matched field observations the model aided the identification of previously unknown steep incised channels active headcuts unstable side walls and a seasonal river flowing near the slopes having large number of landslide scars it was observed that areas that lay on higher elevations where the clusters occur were dominated by fresh scars while the moderate to low elevations were dominated by older ones majority of the slope failures initiated within the sandstone as shallow slides 1 m to the sliding surface covering 104 m2 with short runout distances bigger landslides although few occurred as isolated individual events initiated at the sandstone shale boundary on distinct slopes the steepness of the slopes seemed controlled by slope morphology concavity which probably influenced the number and distribution of landslide events the steeper slopes were more concave and had the highest concentration of scars shallow water table 4 11 m and increased instability brittleness index under increasing over consolidation ratio are the critical failure factors

irrigation induced loess flow failure in heifangtai platform north west china because the construction of dams and hydro electric power stations of liujiaxia and yanguoxia across the yellow river in west gansu province north west china inhabitants in the reservoir areas were resettled in heifangtai loess platform irrigation thus started in 1968 perched water table was significantly raised and resulted in many loess flow failures in the past 30 years this type of landslide was often featured by long runout distance high speed and recurrence laboratory tests along icu and csd stress paths were performed it is shown that the loess has a strong strain softening behavior and instability can occur in drained condition before undrained liquefaction the failure mechanism of loess flow can be interpreted as the following process with increasing perched water table collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform under gravity loading applied by upper dry loess undrained flow failure mobilized eventually

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

modeling the stability of terraced slopes an approach from valtellina northern italy this study focuses on the relationships between hydrological processes and the stability of terraced slopes emphasis is given to the presence of dry stone retaining walls and how to explicitly consider them when performing a distributed stability analysis valtellina an alpine valley of northern italy is selected as study area in detail the slope uphill the village of tresenda affected by several superficial landslides since 1983 is studied dry stone walls heavily influence the hydrological and geotechnical processes at the slope scale and it is therefore crucial to consider them when performing a stability analysis on mountainous terraced areas walls are usually 0 60 1 00 m wide and therefore base maps digital elevation models and soil depth map with a horizontal resolution of 1 m have been appositely derived working at this horizontal resolution leads to the failure of some basic assumptions of the infinite slope method usually applied for distributed stability analysis in this study we propose an alternative approach based on the global method of equilibrium applied to sections of single terraces one cell wide a specific sensitivity analysis allowed to fix some constrains to the model in order to improve the reliability of the results under different mechanical and hydrological conditions the proposed stability model was calibrated and evaluated on recorded past rainfall events it resulted to be a good instrument for the identification of the most unstable areas when stressed with high pore water pressure conditions

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

precise re os ages of organic rich mudrocks and the os isotope composition of jurassic seawater rhenium and osmium isotope and abundance data have been obtained on precisely located samples from three suites of immature organic rich mudrocks from jurassic coastal outcrops in england the data provide accurate whole rock ages of 207 12 ma 181 13 ma and 155 4 3 ma for suites of hettangian toarcian exaratum subzone and kimmeridgian sensu anglico wheatleyensis subzone samples these new re os ages are indistinguishable within the assigned analytical uncertainties from interpolated depositional ages estimated from published geological timescales and establish the importance of the re os dating technique for chronostratigraphic studies early diagenetic pyrite nodules possess levels of re and os which are 1 2 orders of magnitude lower than in the enclosing organic rich mudrocks indicating that these elements had already been removed from sediment pore waters at the time of nodule formation thus the re os isotope system in these organic rich mudrocks has been closed since or from very soon after the time of sediment deposition because most of the re 98 and os 95 99 8 in the mudrocks is shown to be hydrogenous the 187os 188os i of the samples is interpreted to be that of contemporaneous seawater the data thereby provide the first estimates of the os isotope composition of jurassic seawater during the earliest jurassic hettangian the seawater 187os 188os ratio was extremely unradiogenic 0 15 it had increased to 0 8 at the end of the early jurassic toarcian 20 ma later while in the late jurassic kimmeridgian the seawater 187os 188os ratio was 0 59 the most likely explanation for the unradiogenic os isotope composition of hettangian seawater is that the contribution of unradiogenic os to the oceans from the hydrothermal alteration of oceanic crust greatly exceeded the input of radiogenic os from the continents at that time this interpretation is in line with observations suggesting that global weathering rates were low in the hettangian and that increased hydrothermal and volcanic activity preceded the break up of pangea the re os ratios of hettangian mudrocks and by inference of contemporaneous seawater are similar to those of mudrocks deposited at later times during the jurassic and argues against the unradiogenic os in hettangian seawater being derived from extraterrestrial meteoritic sources

estimation of coda wave attenuation in the central and eastern alborz iran the quality factor of coda q c waves has been estimated by using single backscattering and single isotropic scattering models the earthquakes used were recorded by three permanent and one temporary network located in the central and eastern alborz iran the database was composed of 746 local earthquakes with local magnitude from 1 1 to 5 7 the estimated q c has been found to be similar for lapse times greater than twice the s wave travel time 2 t s for both methods the estimated q c for central frequencies 1 0 hz shows less frequency dependency compared with the higher frequencies by using a q f n relation the average frequency dependence of q c for the whole area has been estimated as 59 f 1 03 69 f 0 97 78 f 0 97 105 f 0 93 123 f 0 89 159 f 0 79 and 203 f 0 68 for central lapse times 30 40 50 65 85 110 and 155 s respectively we found the value of q decreases at an average depth of 78 km which may be the result of high dissipating media at this depth the average q c values estimated for central and eastern alborz and their frequency dependent relationships are similar to those of tectonically active regions

14c ages and activity for the past 50 ka at volcan galeras colombia abstract volcan galeras is the southernmost colombian volcano with well recorded historic activity the volcano is part of a large and complex volcanic center upon which 400 000 people live historic activity has centered on a small volume cone inside the youngest of several large amphitheaters that breach the west flank of the volcano away from the city of pasto population 300 000 lava flows sio2 between 54 6 and 64 7 wt have dominated activity for more than 1 ma but explosive events have also occurred joint studies by volcanologists from colombia ecuador peru bolivia argentina and the united states produced 24 new14c ages and more than 100 stratigraphic sections to interpret the past 50 ka of activity at galeras including sector collapse events the youngest collapse event truncated 12 8 ka lava flows and may have occurred as recently as 8 to 10 ka tephra fall material rapidly thins and becomes finer away from the vent area the only widespread marker in the

a reevaluation of cosmogenic 36cl production rates in terrestrial rocks we have measured 36cl in a suite of 33 rock samples having well constrained exposure histories and ages the 36cl production parameters were estimated by minimizing the squared deviations between the 36cl and independent ages yielding the following production parameters spallation and muon production from ca 2940 200 atoms 36cl mole ca 1 yr 1 spallation from k 6020 400 atoms 36cl mole k 1 yr 1 and neutron production in air 586 40 fast neutrons g air 1 yr 1 the new production constants for spallation on ca and thermal neutron activation are in good agreement with previous results but that for spallation on k is about 50 larger the past decade has seen a rapid growth in the application of terrestrial cosmogenic nuclides produced by cosmic ray particles within rocks at the earth surface nuclear cross sections particularly for reactions initiated by neutrons and muons are not known with sufficient accuracy so production rates for these nuclides must be empirically calibrated using independently dated geological samples direct production estimates for 36cl were first obtained by zreda et al 1991 who measured 36c1 in mineral separates from granitic boulders on moraine crests at chiatovitch creek in the eastern white mountains of california and nevada this data set was the best available at the time but since then several factors have prompted a reevaluation of the 36cl production rates one is that zreda et al 1994 have shown that there can be significant scatter of the cosmogenic ages of individual glacial boulders toward ages younger than that of the moraine due to soil erosion a second factor is that a much wider range of samples is now available for this purpose finally recent theoretical advances in calculating production by thermal neutron absorption liu et al 1994 now permit more realistic calibration of this reaction

cosmogenic chlorine 36 chronology for glacial deposits at bloody canyon eastern sierra nevada deposits from mountain glaciers provide an important record of quaternary climatic fluctuations but have proved difficult to date directly a chronology has been obtained for glacial deposits at bloody canyon california by measurement ofthe accumulation of chlorine 36 produced by cosmic rays in boulders exposed on moraine crests the accumulation ofchlorine 36 indicates that episodes of glaciation occurred at about 21 24 65 115 145 and 200 ka thousand years ago although the timing of the glaciations correlates well with peaks of global ice volume inferred from the marine oxygen isotope record the relative magnitudes differ markedly the lengths of the moraines dating from 115 ka and 65 ka show that the early glacial episodes were more extensive than those during the later wisconsin and indicate that the transition from interglacial to full glacial conditions was rapid

comments on separation of qi and qs from passive data at mt vesuvius a reappraisal of the seismic attenuation estimates by e del pezzo et al 2006 in this comment we point out two approximations considered by del pezzo et al del pezzo e bianco f zaccarelli l 2006 separation of qi and qs from passive data at mt vesuvius a reappraisal of the seismic attenuation estimates phys earth planet int 159 202 212 for estimating intrinsic absorption and scattering attenuation in vesuvius volcano region the first one is the theoretical model used for calculating the synthetic s wave envelopes for the case of multiple scattering the second one is based on the stacking of coda envelopes we consider that both assumptions have no general validity for this kind of analysis and thus may have biased their results

the relationship between 10be and geomagnetic field strength records in central north atlantic sediments during the last 80 ka abstract a profile of leached 10 be 9 be has been measured in an 80 ka sediment core from the northeast atlantic ocean this profile shows a significant inverse correlation with the palaeomagnetic intensity profile inferred from nrm arm measurements in the same core particularly between 40 and 50 ka where a rapid decrease in field intensity is accompanied by a rapid increase in 10 be 9 be the extent to which this increase in 10 be 9 be at 40 ka is associated with a 10 be peak seen in polar ice cores at about the same time remains speculative