qlg tomography in colombia the crustal attenuation of lg waves in colombia was estimated and analyzed using local seismological data from the national seismological network of colombia rsnc the selected dataset comprises 510 crustal earthquakes with a total of 2928 ray paths this large dataset allowed us to invert for a regional average of qlg tomographic images for colombia and simultaneously source size for each event and site term at the seismological stations the computed regional average for qlg in the frequency band 0 5 5 0 hz was found to agree with the previously reported values in neighboring regions in order to resolve the lateral variation in the attenuation of lg waves in the crust independent tomographic inversions for 26 frequencies between 0 5 and 5 0 hz were conducted the resulting maps confirm that heterogeneities in the crust exist and that they are related to the large scale tectonic features in the country the highest attenuation in the region is linked to the presence of active volcanic arcs where the crust is weakened by partial melting relatively high attenuation is also found in zones where the crust is composed of accreted oceanic rocks and in regions with near surface low velocity sedimentary layers 2002 elsevier science b v all rights reserved

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

an environmental reconstruction of the sediment infill of the bogota basin colombia during the last 3 million years from abiotic and biotic proxies abstract the lacustrine sediments of the intramontane basin of bogota 4 n 2550 m altitude were collected in a 586 m deep core funza 2 absolute datings show sediment infill started c 3 2 ma and continued almost without interruptions as a result of the balance between tectonic subsidence and sediment infill analysis of downcore changes in lithology grain size facies loss on ignition loi and hydrosere vegetation at 20 cm intervals along the core produced a 2200 sample record of basin dynamics and lake level changes with a temporal resolution from c 800 years during the last 1 5 ma to c 2000 years from 1 5 to 3 2 ma we recognized 11 discrete sedimentary facies that reflect 4 different depositional environments facies 1 and 2 correspond to lacustrine environment where the loi is 20 a fluvio lacustrine environment is represented by the facies 3 4 5 7 and 9 a fluvial environment is reflected by facies 6 8 and 10 basin infill started with accumulation in a fluvio lacustrine environment between 586 and 530 m below the present day sediment surface of the basin in the 530 to 325 m interval c 3 1 5 ma the basin contained mainly shallow water and swamps in combination with some fluvial activity the 325 5 m interval 1 5 0 028 ma shows almost uninterrupted lacustrine paleoenvironmental conditions the uppermost 5 m reflect a fluvial paleoenvironment deposited by the bogota river and its tributaries the downcore changing ratio between shallow water aquatics myriophyllum ludwigia polygonum cyperaceae and aquatics of deeper water isoetes is indicative of lake level changes isoetes as an indicator of high water levels is not consistent with fluvial and fluvio lacustrine depositional regimes several lithological discontinuities evidenced by the sharp transition from swamp deposits to fluvio lacustrine and fluvial deposits are present in the core in the interval from 530 to 325 m in particular it is plausible that swamp deposits have been eroded during episodes during which the water table quickly raised or during events of sudden coarse fluvial input into the basin

sources and reservoirs of anthropogenic iodine 129 in western new york large quantities of iodine 129 have been released during nuclear weapons testing and from nuclear power and fuel reprocessing plants the distribution of this isotope was investigated in 110 surface water and soil samples from western new york where several potential point sources are located and other areas of north america to evaluate its sources transport pathways and reservoirs elevated 129i concentrations associated with a former reprocessing facility at west valley ny can be tracked to lakes erie and ontario via site drainage and for over 200 km via atmospheric transport while only a negligible signal is associated with active power plants in the area the results point to local reprocessing as the major source of 129i in western new york while bomb fallout constitutes less than 0 5 of the signal surface soil is the dominant reservoir for anthropogenic 129i in this region across north america 129i concentrations are lower than in western new york although still significantly higher than expected weapons fallout reprocessing releases are currently seen to be the major source for elevated 129i concentrations on a global scale in contrast to previous suggestions that most anthropogenic 129i was still derived from weapons fallout concentrations of 129i and iodine in surface reservoirs are generally found to be uncorrelated implying that natural iodine and anthropogenic 129i are not yet in equilibrium the results suggest that anthropogenic 129i is cycled between the atmosphere soil vegetation systems more rapidly than natural pre anthropogenic iodine

contributions of basin edge induced surface waves to site effect in the dinar basin southwestern turkey ground motion amplifications in the dinar basin and contributions of the surface waves generated from basin edges are investigated in frequency and time domains amplification functions are computed from the aftershock data of the october 1 1995 dinar earthquake mw 6 4 using the standard spectral ratio method which requires a pair of instruments one located at the site under investigation generally on alluvium and the other on a reference site preferably a nearby rock site first a time window covering the whole signal is used to compute the amplification function and successively the noise p wave s wave and the surface wave time windows are used in computation to observe their contributions to the amplification function it is seen that the maximum amplifications observed at about 2 0 hz on the amplification functions of the stations located in the basin are largely due to basin edge induced surface waves these waves have significantly increased the duration of signals recorded within the basin particularly on the vertical component records the amplitudes of surface waves are larger than the s wave amplitudes the periods of waves amplified maximally due to the basin structure coincide with the natural periods of 4 6 story buildings which were heavily damaged in dinar this indicates that the site effects may have been important regarding the damage which occurred during the dinar earthquake of october 1995

a microstructural investigation of osaka bay clay the impact of microfossils on its mechanical behaviour a recent microstructural investigation of osaka bay clay sediments has revealed the presence of abundant microfossils particularly in the marine layers which appear to influence directly the micr

a vs30 map for california with geologic and topographic constraints abstract for many earthquake engineering applications site response is estimated through empirical correlations with the time averaged shear wave velocity to 30 m depth v s 30 these applications therefore depend on the availability of either site specific v s 30 measurements or v s 30 maps at local regional and global scales because v s 30 measurements are sparse a proxy frequently is needed to estimate v s 30 at unsampled locations we present a new v s 30 map for california which accounts for observational constraints from multiple sources and spatial scales such as geology topography and site specific v s 30 measurements we apply the geostatistical approach of regression kriging rk to combine these constraints for predicting v s 30 for the v s 30 trend we start with geology based v s 30 values and identify two distinct trends between topographic gradient and the residuals from the geology v s 30 model one trend applies to deep and fine quaternary alluvium whereas the second trend is slightly stronger and applies to pleistocene sedimentary units the rk framework ensures that the resulting map of california is locally refined to reflect the rapidly expanding database of v s 30 measurements throughout california we compare the accuracy of the new mapping method to a previously developed map of v s 30 for california we also illustrate the sensitivity of ground motions to the new v s 30 map by comparing real and scenario shakemaps with v s 30 values from our new map to those for existing v s 30 maps online material california statewide v s 30 and shakemaps for loma prieta

study of the structure of a sensitive champlain clay and of its evolution during consolidation scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity champlain clay the clay structure is observed firstly on intact remolded and oven dried soils and secondly on soils consolidated at various levels in one dimensional compression both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra aggregate porosity remolding affects interaggregate links but does not destroy aggregates the observation of clay structure at various levels of one dimensional compression shows that the collapse of the structure is progressive the largest interaggregate pores being the first affected as the consolidation proceeds smaller and smaller pores are affected for a given pressure increment only the largest existing pores are affected a structure anisotropy has been seen to develop with increasing compression the scanning electron microscope and the me

the influence of humic substances on the geochemistry of iodine in nearshore and hemipelagic marine sediments iodine is characteristically enriched at the surface of hemipelagic and nearshore sediments deposited under oxygenated conditions in such sediments bulk i corg ratios usually decrease with depth to values which are characteristic of anoxic sediments reflecting a preferential release of i during early diagenesis there is some debate as to whether sedimentary i is associated with the iron oxyhydroxide phase or with the organic fraction and whether the decrease in i corg with depth is due to the dissolution of the iron oxyhydroxides or the decomposition of labile organic matter it is shown that in a surficial hemipelagic sediment sample and in a nearshore sediment core i is mainly associated with the organic fraction and moreover that humic substances are involved in the surficial iodine enrichment laboratory experiments on the uptake and release of i by and from sedimentary humic substances also suggest a mechanism whereby humic materials reduce iodate at the sediment water interface to an electrophilic i species which further reacts with the organic matter to produce iodinated organic molecules during burial this excess i could be displaced from the organic matrix by nucleophiles such as sulphide ions or thiosulphate thus providing a possible explanation for the decrease in i corg ratio with depth observed in many nearshore and hemipelagic sediments

undrained shear strength of pleistocene clay in osaka bay this study presents the undrained shear characteristics of holocene and pleistocene clay samples from depths of 20 200 m under the seabed in osaka bay automated triaxial k0 consolidation tests and anisotropically consolidated undrained triaxial compression and extension tests are conducted using the recompression method the average undrained strength ratio su v0 is 0 33 sd 0 03 when the extension strength is defined as the peak strength or the strength at an axial strain of 15 while su v0 is 0 29 sd 0 04 when the extension strength is defined as the shear stress at the axial strain corresponding to the peak compression strength circular arc stability analyses are carried out with the modified fellenius and bishop methods for the design cross section of the seawall structure of the kansai international airport to study the effects of different definitions of shear strength the seawall is founded on 19 m of soft holocene clay and 10 m of pleistocene sand overlying the pleistocene clay the s

using halogens cl br i to understand the hydrogeochemical evolution of drought derived saline porewater beneath a prairie wetland abstract numerous closed basin prairie wetlands throughout the prairie pothole region ppr of north america maintain moderate surface pond salinities total dissolved solids tds from 1 to 10 g l 1 under semiarid climate by accumulation of gypsum and saline lenses of sulfate rich porewater tds 10 g l 1 in wetland sediments during droughts in order to understand the hydrogeochemical origin and composition of these saline porewaters we made a detailed geochemical survey of cl so42 br and i in the porewater pondwater and upland groundwater of a typical closed basin prairie wetland p1 in the cottonwood lake study area north dakota concentrations of cl ranged up to 5 9 mm in the saline porewaters and was strongly correlated with so42 and br pearson s r 0 7 p

compressibility and creep of a diatomaceous soil abstract diatomaceous soils are composed by a mix of sand fines and fossilized diatoms which are unicellular microalgae composed by a strong silica frustule of 10 to 100 m in size with rough surface and enclosing a void that could give the soil a very low dry density due to high water storage capacity within frustules diatomaceous soils present high liquid limit and classifies as high plastic silt mh in classical soil mechanics low density and high plasticity are properties associated to very soft soils however previous studies have reported that diatomaceous soils could mobilize high shear strength and present relatively high yield stress due to large diversity of natural diatomaceous soils in nature their geotechnical singularities are still not fully understood and reported data on undisturbed samples remain scarce in this paper a laboratory experimental study is presented on a diatomaceous soil from mejillones bay in northern chile focused on compressibility and creep microscopic observations and mineralogical analyses indicate that the soil contains siliceous diatom frustules of 10 to 60 m in size which gives the soil a very low dry density and high natural water content compression tests on undisturbed samples results in yield stress much higher than the overburden pressure high contrast between compressibility before and after yielding and significant creep strains the diatomaceous soil does not follow empirical correlations typically used in soil mechanics and is significantly more compressible than fine soils with similar geotechnical classification qualitative microscopic observations after compression show that a large amount of frustules have crushed which probably explains the high compressibility of the soil

singularities of geotechnical properties of complex soils in seismic regions volcanic activity results in a wide range of soil types with very unusual characteristics the most remarkable of which are volcanic ash clays containing the clay minerals allophane and imogolite in addition to these soils volcanic activity often produces the special environmental conditions that result in the formation of diatomaceous soils namely water rich in dissolved silica these soils consist of individual particles containing intraparticle voids filled with water resulting in a very unique porous particle morphology that is quite different than stereotypical sedimentary soils this paper presents a series of careful laboratory tests on samples of both materials found in chile these tests demonstrate that soils weathered from volcanic ash develop yield pressures that are similar to the preconsolidation pressure of sedimentary soils this type of soil also shows a dramatic change in properties due to drying in addition diatomaceous soils and those containing allophane have very low densities in spite of which they develop remarkably high shear strength the need for their properties to be properly understood and taken into account in geotechnical design especially seismic design is emphasized since the location of these soils generally coincides with earthquake activity which like volcanic activity arises from tectonic plate interaction

soil structure of a highly weathered old alluvium the old alluvium in san juan puerto rico is an early pleistocene deposit that has undergone substantial post depositional weathering in a tropical climate preliminary geotechnical laboratory testing found that the soil exhibits some unusual index and consolidation properties compared with stereotypical sedimentary soils for instance both the swelling index and the coefficient of consolidation are greatly affected by the maximum past stress applied to the soil in order to understand its unusual behaviour a variety of experiments were performed to characterise its composition and microstructure direct observations of the microstructure used environmental scanning electron microscopy and indirect examinations included slaking cation exchange capacity selective chemical dissolution particle size analyses and atterberg limits the results clearly indicate that the weathered deposit possesses a complex microstructure the intact material consists of a stiff network of aggregates interconnected by fe

anomalous propagation of long period ground motions recorded in tokyo during the 23 october 2004 mw 6 6 niigata ken chuetsu japan earthquake unusually large 5 cm and prolonged shaking associated with long period ground motions at periods of about 7 sec were observed in central tokyo during the mw 6 6 niigata ken chuetsu earthquake of 23 october 2004 the long period ground motions caused significant resonance in high rise buildings of about 70 floors in height thus it is an urgent matter to understand the development and amplification properties of long period ground motions in tokyo associated with large earthquakes in this study we use numerous waveform records from 585 stations in a nationwide accelerometer network k net kik net and 495 intensity meters in the area around tokyo the data reveal that the long period ground motion is characterized in most part by a surface rayleigh wave generated at the northern edge of kanto basin and the surface wave is developed as propagating through a thick cover of sediments 3000 4000 m that overlies rigid bedrock to complement the observational data we conducted a large scale computer simu lation of seismic wave propagation by employing the earth simulator supercomputer with a detailed source slip model and a high resolution 3d sedimentary structural model of central japan the results of the computer simulation demonstrate that the anomalously prolonged ground shaking of the long period signal recorded in the center of tokyo occurred because of the stagnation of seismic energy resulting from the multipathing and focusing of rayleigh waves toward the bottom of the kanto basin from surrounding mountain regions with interaction to the 3d basin structure

physical chemical and mineralogical properties of mexico city sediments a geotechnical perspective the authors appreciate the interest of the discussers in the paper and offer the following comments as indicated in the paper the results presented were obtained as part of a comprehensive research program on the microstructure of mexico city sediments being conducted at the national university of mexico a second site has been studied and the corresponding paper has been written in which correlation of the profiles of geotechnical properties of the sediments with their profiles of physical chemical and mineralogical properties has been investigated the discussers compare the mexico city sediments with illitic sensitive clays in canada the united states and norway we believe their discussion estimates in an alternate scenario which did not in our judgement optimally represent the circumstances of the just case the focus of our article principally mexico city sediments are predominant disintegration products of andesitic rocks and fine and ultrafine volcanic ash furthermore the discussers indicate that variations in carbonate content may have only a small influence on observed variations in the engineering behavior of deposits with high water content which is the case for mexico city sediments all of the ramon lopez velarde park core was checked with scanning electron microscopy and we did not find carbonate precipitation except at a depth of 4 m from the surface so the role of carbonate cementation is doubtful phase contacts are developed in highly compacted clays or cemented clays and are distinguished by the presence of direct contacts between the structural elements and by a new phase carbonates developed at the contacts cementing the particles coagulation contacts are widespread in young clays and poorly cemented clays the structural elements do not directly touch each other and structural cohesion is de termined by molecular and possibly magnetic and dipole interaction furthermore the coagulation contacts allowed the soil to reach a restructured form after it was altered which happened in the mexico city sediments the authors agree that the processes by which the amorphous material content is determined are chemically aggressive as suggested by the discussers overall however the authors feel that the role of the amorphous material is mainly responsible for the properties of mexico city sediments the authors will investigate further quantitative interpretations in mexico city sediments

the speciation of iodine in the salt impacted black butte soil series along the virgin river nevada usa abstract salt impacted soils occur in floodplains wetlands and backswamps in arid climates these soils become sinks or temporary storage sites for soluble salts and contaminants including agricultural chemicals industrial pollutants and radionuclides such as 129i the vertical distribution of i in the black butte soil series along the virgin river was assessed and the distribution of i between i io 3 and organically bound i was determined the speciation of i was compared to the organic c content specific components of the organic c and clay content this study indicates that organic i was the most abundant form of i in these soil samples and that the content of organic i generally correlated to total organic matter and lignin as measured by chemolysis of the samples

the 129iodine bomb pulse recorded in mississippi river delta sediments results from isotopes of i pu cs pb and c 129i t1 2 1 56 107 yr has both natural as well as anthropogenic sources anthropogenic sources from nuclear reprocessing discharges and bomb test fallout have completely overwhelmed the natural signal on the surface of the earth in the last 50 years however the transfer functions in and out of environmental compartments are not well known due to temporal variations in the sources of 129i and to a lack of knowledge regarding the forms of iodine from a vertical profile of 129i 127i ratios in sediments located in the mississippi delta region in approximately 60 meters water depth the 129i input function to this region was reconstructed dates in the core were assigned based on the plutonium peak at 20 cm depth assumed to have been deposited in 1963 and the excess 210pb profile in the same depth interval and below that based on the steadily decreasing 240pu 239pu ratios from a ratio of 0 18 at 22 cm to 0 05 at 57 cm depth the 1953 horizon these low 240pu 239pu values are attributed to low yield close in tropospherically transported bomb fallout produced from the nevada test site in the early 1950s which had a value of about 0 035 and strongly suggest a terrestrial source for pu isotopes 129i 127i ratios increased from 2 10 10 at 3 cm to 4 10 10 at 20 cm and from there decreased monotonously to pre anthropogenic values at 53 cm and below 129i concentrations ranged from 8 13 106 atoms g in the top 20 cm and decreased to values of less than 1 106 atoms g below 50 cm atom ratios of 129i 137cs decay corrected to 1962 the year of maximum radionuclide production are about 0 3 very close to the production ratios of about 0 2 during atomic bomb tests this evidence combined with other observations strongly suggests that 129i in mississippi river delta sediments originates from atomic bomb fallout eroded from soils of the mississippi river drainage basin with little alteration of the isotopic ratios during transport from watershed to coastal deposits this is further corroborated by a close correspondence between 129i 127i ratios and other bomb fallout nuclides in this core based on these observations and on laboratory evidence we propose a conceptual model which explains this correspondence and the low 129i 127i ratios found in our sediment core as caused by geochemical i isotope fractionation processes during organic carbon leaching from erodible soils in the mississippi river watershed differences in mobilities of the different chemical forms of 129i and 127i as well as the variances in chemical forms of 129i from nuclear bomb fallout versus nuclear fuel reprocessing are proposed to have created such a correspondence between i isotope ratios and bomb fallout nuclides without revealing recent inputs from nuclear fuel reprocessing releases to the northern hemisphere observed in watersheds of the usa and europe

empirical models for surface and body wave amplifications of response spectra in the bogota basin colombiaempirical models for surface and body wave amplifications of response spectra in the bogota basin