magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

three dimensional finite difference waveform modeling of strong motions observed in the sendai basin japan we perform three dimensional 3d finite difference fd waveform modeling of strong motions in the frequency range 0 2 to 1 67 hz observed in the sendai basin japan during the japan meteorological agency magnitude m j 5 0 1998 miyagiken nanbu earthquake in a previous we estimated s wave velocity structures above the pre tertiary bedrock at six sites in the sendai basin based on array records of microtremors to interpolate these velocity structures in space we conduct single station microtremor measurements at a total of 61 locations and estimate the s wave velocity structure at each site by modeling the horizontal to vertical spectral ratio of fundamental mode rayleigh waves an initial 3d model of the basin is constructed using the velocity structures estimated from both array and single station microtremor measurements along with other information such as surface geology this model encompasses a region 33 km long 30 km wide and 19 km deep the final model is obtained through a trial and error process by fitting 3d fd synthetic waveforms to the bandpass filtered 0 2 hz to 1 67 hz displacement records 12 stations for the 1998 miyagiken nanbu earthquake we compute the synthetics using a fourth order staggered grid 3d fd method with variable grid spacing as the 3d model is modified the source parameters strike dip rake and seismic moment are estimated by a grid search method using 1d site specific models derived from the modified 3d model the observed waveforms are reproduced well at most stations by the final 3d basin model this agreement suggests the validity of the final 3d basin model for theoretical strong motion prediction of large earthquakes in the frequency range from 0 2 to 1 67 hz manuscript received 7 june 2000

seismic waves estimation and wavefield decomposition application to ambient vibrations summary passive seismic surveying methods represent a valuable tool in local seismic hazard assessment oil and gas prospection and in geotechnical investigations array processing techniques are used in order to estimate wavefield properties such as dispersion curves of surface waves and ellipticity of rayleigh waves however techniques presently in use often fail to properly merge information from three components sensors and do not account for the presence of multiple waves in this paper a technique for maximum likelihood estimation of wavefield parameters including direction of propagation velocity of love waves and rayleigh waves and ellipticity of rayleigh waves is described this technique models jointly all the measurements and all the wavefield parameters furthermore it is possible to model the simultaneous presence of multiple waves the performance of this technique is evaluated on a high fidelity synthetic data set and on real data it is shown that the joint modelling of all the sensor components decreases the variance of wavenumber estimates and allows the retrieval of the ellipticity value together with an estimate of the prograde retrograde motion

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

paleoclimatic significance of the mineral magnetic record of the chinese loess and paleosols the origins of the magnetic susceptibility variations of the chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts and by magnetic modeling of magnetic hysteresis data to provide quantified estimates of the major magnetic components microscopy identifies several distinct size and shape characteristics in the magnetic carriers lithogenic magnetites intact and abraded dominate the coarse grained magnetic fraction the smallest of the coarse grains is 2 i m the remaining magnetic materal is ultrafine in size with two types of magnetite particles present type a particles strongly resemble soil magnetites produced by inorganic precipitation type b particles which occur rarely are probably bacterial in origin quantitative modeling of these magnetic assemblages shows that over 90 of the susceptibility variations is accounted for by the superparamagnetic magnetite component compared to the loess units the paleosols are richer in magnetite particularly of superparamagnetic size and have a threefold higher ratio of magnetite to hematite we identify pedogenic formation of magnetite as the major contributor to the loess magnetic record matching this record against other paleoclimatic records we find an extremely high correlation with the standard 18o record the chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate

ambient vibration classification of unstable rock slopes a systematic approach abstract in this paper we are comparing the seismic response of 25 different rock slope instabilities with diverse geological properties activity level failure mechanism fracturing and volumes we classify them according to their dynamic behaviour in the dataset we found two main classes of unstable rock slopes depth controlled sites and volume controlled sites for depth controlled instabilities the seismic wavefield is controlled by horizontally propagating surface waves in the highly fractured and weathered material at such sites surface wave dispersion curves can be retrieved and inverted into velocity profiles of the underground the lateral borders of depth controlled instabilities are not obvious and the seismic properties mainly change with depth the seismic response of volume controlled sites is dominated by the eigenvibrations of the rock mass itself such instabilities have clear lateral and vertical borders and show highly amplified ground motion in limited frequency bands the observed polarisation of the ground motion is perpendicular to deep open fractures that do not allow surface waves to propagate a special case of the volume controlled sites is represented by tower like rock masses showing strong amplification and directionality their dynamic behaviour might not only be related to the internal structure but also to their geometry that is similar to high rise buildings another type of rock instabilities is represented by block structures which are difficult to identify by the proposed ambient vibration methods a clear relation between geological properties and seismic response was not found

3 d simulations of surface wave propagation in the kanto sedimentary basin japan part 2 application of the surface wave bem abstract the 3 d surface wave boundary element method is applied to the same set of strong motion records as those of part 1 kato et al 1993 namely the long period strong motion with periods around 8 sec recorded at the jma japan meteorological agency stations in yokohama and tokyo during the 1980 izu hanto toho oki earthquake this method simulates exact love and rayleigh waves in a laterally heterogeneous medium including 3 d basin structures the needed computer memory and cpu time are made manageable by assuming the inside and outside of the basin to consist of horizontal flat layers in addition vertical interfaces are assumed between the basin and the outside bedrock for simplicity in this study after checking the range of validity of the flat layer approximation for the kanto sedimentary basin the generation and propagation of surface waves in the basin are numerically investigated in particular our investigation places special emphasis on the cause of the observed long duration which could not be explained in part 1 using the surface wave gaussian beam method when the bedrock outside the western margin of the kanto basin is incorporated into the model the observed long duration at the tokyo station is successfully reproduced this can be explained by the strong surface waves generated by the surface wave to surface wave conversion at the margin and appearing in tokyo after the direct surface waves from the epicenter this result agrees with kinoshita et al 1992 who studied records from an array of seismographs in tokyo moreover when a sedimentary basin of sagami bay is included as was done in part 1 the simulations are greatly improved particularly at the yokohama station which corresponds to the node in the radiation pattern of the source this is due to the fact that the radiation pattern is strongly affected by the near source heterogeneity of the sagami basin all these results together with direct comparisons to 2 d modelings clearly show the strong 3 d effects of the basin structures on the generation and propagation of surface waves for this earthquake

effect of burial and compaction on soil magnetic properties results from soil paleosol sequences in the himalayan foreland india abstract the study based on 395 stratigraphically ordered pedogenic and associated non pedogenic horizons in the himalayan foreland basin indicated a significant depth control for the routine rock magnetic parameters lf fd arm sirm b cr and s ratio the study representing eight fluvial sections with overburdens varying from 0 to 5 km for holocene to 11 ma interval spread over an area of 9000 km 2 infer at least three major phases of mineral magnetic response to soil physico chemical changes these are phase i early burial compaction dissolution and diagenetic changes up to an overburden of 1 5 km leading to substantial loss in ultra fine pedogenic ferrimagnetic oxides phase ii late burial diagenetic transformations up to 2 5 km of overburden leading to formation of antiferromagnetic oxides probably accelerated by the high crustal heat flows of the region and phase iii development of stable antiferromagnetic phase after 2 5 km of burial consequent to phase ii these results indicate a greater control of burial related changes over the routine mineral magnetic parameters than that due to paleoclimatic variations for paleosols of 1 5 km overburden or 2 ma of age in the himalayan foreland basin

three dimensional finite difference simulations of long period strong motions in the tokyo metropolitan area during the 1990 odawara earthquake mj 5 1 and the great 1923 kanto earthquake ms 8 2 in japan utilizing a crustal velocity model that includes the complexity of the irregular subsurface structure of the kanto basin we have performed three dimensional 3d finite difference fd simulations of near source long period strong ground motions in the tokyo metropolitan area for the 1990 odawara mj 5 1 and the 1923 kanto ms 8 2 earthquakes constraints on the development of the 3d velocity model come from available geological and geophysical data as well as our previous 1d waveform modeling results sato et al 1998a the simulation of the moderate sized odawara earthquake demonstrates that the 3d velocity model works quite well at reproducing the recorded long period t 3 33 sec strong motions including basin generated surface waves for a number of sites located throughout the kanto basin region using this validated 3d model along with the variable slip rupture model of wald and somerville 1995 we then simulate the long period t 4 sec ground motions in this region for the 1923 kanto earthquake the simulation results for the 1923 event show that the largest ground motions occur east of the epicenter along the central and southern part of the boso peninsula these large motions arise from strong rupture directivity effects and are comprised of relatively simple source controlled pulses with a dominant period of about 10 sec north of the epicentral region in the tokyo area 3d basin generated phases are quite significant and these phases produce large amplitude late arriving pulses in the ground motions at station hongo hng which is the only site having digitized and restored near fault strong motion records for this event our 3d simulations compare quite well with the ground motions of the restored imamura seismogram for the restored ewing record our 3d simulations reproduce the phase and amplitude of the initial pulses of motion however the dominant period of the large amplitude later phases is noticeably shorter in the simulations about 5 to 6 sec than in the observation 13 sec these results suggest that the restored imamura seismogram may be a better representation of the gross features of the actual motion than the restored ewing seismogram although the first clipped and restored part of the imamura seismogram may still underestimate the strength of the actual motion

role of pedogenesis in distribution of magnetic susceptibility in two california chronosequences abstract pedons from two soil chronosequences from coastal terraces in northern california were examined and sampled and samples were analyzed to determine the contribution of normal pedogenic processes to the distribution of mass magnetic susceptibility in soils commonly distribution in soils and the formation of susceptibility enhancement in near surface soil layers are attributed in large part to the in situ conversion of nonferrimagnetic iron oxides and oxyhydroxides to microcrystalline ferrimagnetic minerals solubilization of fe 2 and subsequent precipitation also contribute to enhancement we show that enhancement occurred throughout the eluvial and in some illuvial horizons to depths as great as 100 cm in these soils eluvial horizon and enhancement increased with increasing soil age the enhancement of magnetic susceptibility resulted from the accumulation of pedogenic ferrimagnetics and the preferential accumulation of both inherited magnetite and pedogenic maghemite we use the differential solubility of inherited magnetite and maghemite in citrate bicarbonate dithionite and x ray diffraction to distinguish between the two minerals although magnetite is a relatively more durable soil mineral it did weather and the total amount of magnetite decreased as soil age increased sonicated sand grains free of clay or fe coatings contributed to susceptibility enhancement silt and clay sized grains provided the larger part of illuvial horizon illuviation to or formation of clay sized ferrimagnetic particles in illuvial horizons probably reduced the observed eluvial enhancement enhancement of eluvial horizons and distribution throughout the soil oprofiles can be explained by common soil forming processes

magnetic enhancement is linked to and precedes hematite formation in aerobic soil 1 soil formation usually increases magnetic susceptibility most often by increasing the concentrations of magnetite and maghemite which are two ferrimagnetic iron oxides here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite which is later transformed into hematite the iron oxide that gives red color to soil we show that the maghemite hematite ratio is influenced by the particular environment and the degree of soil development so it constitutes an effective tool for paleoenvironmental and planetary studies

array estimators and the use of microseisms for reconnaissance of sedimentary basins a natural field seismic technique is possible to attain by observing microseisms with a suitably designed array and by digitally processing the data to obtain estimates of the phase velocities of rayleigh waves wavelengths of interest in detecting depth to the basement of sedimentary basins are in the range 2 to 20 km and correspond to wave periods from 1 to 7 s an array of five or seven seismometers deployed as an expanding cross configuration simplifies field procedures and is adequate for phase velocity measurements of rayleigh waves in the required wavelength range provided high resolution frequency wavenumber spectral analysis is used this analysis can be implemented on a minicomputer in the field results obtained from observation in a sedimentary basin of known structure show predominantly fundamental mode rayleigh wave propagation the scatter of velocity estimates is small enough to allow inversion by curve matching and depth to the basement can be computed to an accuracy of 30 percent w

vsp beyond time to depth vsp or vertical seismic profile was originally designed and is currently primarily used to give us time to depth for seismic well ties beyond time to depth a number of possibilities exist recently there has been considerable interest in vsp imaging ray et al 2003 paulsson et al 2004 hornby et al 2004 hornby et al 2005a with extensive surveys being acquired both on land and offshore modeling studies using full waveform finite difference method fdm payne et al 1994 van gestel et al 2003 show us what we can image for a particular acquisition geometry and geology with best image results seen with 3d vsp surveys incorporating a large vsp array in the well and a 2d source pattern acquired using a surface seismic shooting vessel traditionally vsp imaging has been implemented using surface seismic processing algorithms however the vsp geometry poses its own challenges and unique opportunities in this article we explore some imaging methods to attempt to take advantage of the vsp g

pedogenic transformation of magnetic minerals in pliocene pleistocene palaeosols of the siwalik group nw himalaya india abstract we present preliminary rock magnetic and geochemical analyses of thirty one pedogenic intervals from six palaeosol profiles in a pliocene pleistocene fluvial sequence of the siwalik group in nw himalaya the palaeosols are characterised by low magnetic susceptibility lf mean 9 10 8 m3 kg low frequency dependent susceptibility fd mean 0 93 high coercivity of remanence b0 cr mean 447 mt and high mean hysteresis ratios mrs ms mean 0 6 as a result of the predominance of imperfect antiferromagnetic minerals hematite and goethite stepwise irm acquisition to 7 t and backfield demagnetisation to 1 t suggest the predominance of goethite in several intervals the relative contributions of goethite and hematite are derived from differential rates of irm acquisition which are further confirmed using stepwise thermal demagnetisation of orthogonal irm components acquired at 4 1 and 0 3 t the absence of a significant superparamagnetic fraction and the apparent depth control of fd are attributed to post depositional processes of compaction and burial diagenesis anomalously high coercivities within the goethite enriched horizons may have resulted from trm acquisition due to the high crustal heat flows due to cumulative burial to depths of over 1 km pedogenically induced magnetic mineral production and transformation within the palaeosol profiles are inferred using a range of rock magnetic parameters geochemical ratios e g rb sr and al si and percentage organic inorganic carbon content we use magnetic ratios based on the relative contributions of goethite hematite and soft ferrimagnetic minerals to infer climate sensitive processes of oxidation reduction hydration dehydration hydroxylation dehydroxylation and humification in the earliest pliocene palaeosol we infer the pedogenic depletion of magnetic susceptibility due to the transformation of parental ferrimagnetic minerals mainly into antiferromagnetic minerals in contrast the youngest middle pleistocene profile shows significant modification of parental antiferromagnetic minerals into ferrimagnetic forms we suggest that further detailed rock magnetic and geochemical studies using a higher sampling density and at a regional scale would help reconstruct the pedogenic transformation of iron oxides in the tropical subtropical siwalik soils and the effect of post depositional and burial processes upon them

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

ambient vibration analysis on large scale arrays when lateral variations occur in the subsurface a study case in switzerland the ambient vibration analysis is a non invasive and low cost technique used in site characterization studies to reconstruct the subsurface velocity structure depending on the goal of the research the investigated depth ranges from tens to hundreds of meters in this work we aimed at investigating the deeper contrasts within the crust and in particular down to the sedimentary rock basement transition located at thousands of meters of depth to achieve this goal three seismic arrays with minimum and maximum interstation distances of 7 9 m and 26 8 km were deployed around the village of schafisheim schafisheim is located in the swiss molasse basin a sedimentary basin stretching from lake constance to lake geneva with a thickness ranging from 800 to 900 m in the north to 5 km in the south to compute the multimodal dispersion curves for rayleigh and love waves and the rayleigh wave ellipticity angles the data were processed using two single station and three array processing techniques a preliminary analysis of the inversion results pointed out a good agreement with the fundamental modes of rayleigh and love waves used in the inversion and a quite strong disagreement with the higher modes the impossibility to explain at the same time most of the dispersion curves was interpreted as the co existence within the investigated area of portions of the subsurface with different geophysical properties the hypothesis was confirmed by the horizontal to vertical spectral analysis h v which indicated the presence of two distinguished areas the observation allowed a new interpretation and the identification of the rayleigh and love wave fundamental modes and of the s wave velocity profiles to be reconstructed for each investigated zone it results in two s wave velocity profiles with similar velocities down to 15 km deferring only in their shallow portions due to the occurrence of a low velocity zone at a depth of 50 150 m at the centre of the investigated area

relations between soil colour and waterlogging duration in a representative hillside of the west african granito gneissic bedrock abstract the purpose of this study was to analyse if the colour of soils on granito gneissic bedrock of west africa could give some simple indicators of the duration of soil waterlogging a toposequence on a representative hillside in central togo lat 8 38 8 39 n long 1 00 1 01 e was studied by means of 19 hydropedological stations soil and piezometric conditions were studied on these stations for three annual cycles 1989 1992 during which rainfall conditions were representative of the mean rainfall conditions for that hillside data collected in each station were used to calculate the mean annual rate of soil waterlogging wlg at 10 cm intervals from the surface down to a depth of 7 m at the same intervals 10 numerical colour variables were calculated from the colours of the uncemented soil phases munsell value chroma angular hue and redness rating of the principal uncemented phase mean munsell value mean chroma mean angular hue and mean redness rating barycentric chroma and barycentric angular hue statistical relationships were established between wlg and each of the variables derived from soil colour 10 574 pairs the two most significant relations were those between wlg on one hand and mean angular hue and mean redness rating on the other these two relationships provided the basis for logistic models for predicting the mean annual rate of soil waterlogging the operational limits of these models are discussed

goethite and hematite in a climosequence in southern brazil and their application in classification of kaolinitic soils abstract the goethite hematite goethite ratio of 11 profiles of oxisols ultisols and inceptisols along a 600 km e w transect in s brazil varied systematically with climatic and soil factors the ratio increased with decreasing mean annual air temperature increasing excess moisture rainfall minus evapotranspiration increasing soil organic carbon and decreasing ph this is explained in light of the current concept of goethite and hematite formation in soils higher temperatures favor hematite whereas higher excess moisture higher organic carbon and lower ph favor goethite a basis is suggested for using goethite and hematite in the mineralogical classes at the family level of soil taxonomy

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

contribution of dense array analysis to the identification and quantification of basin edge induced waves part i methodology recent earthquakes have shown that edge generated surface waves can significantly contribute to increased damages most observations of edge generated surface waves are concerning long period surface waves propagating in large size valleys since travel times of such waves between valley edges can reach several tens of seconds they are quite easy to isolate in small size structures reverberating wave trains are mixed and very dense array analysis is required for the identification of basin induced surface wave trains the city of grenoble french alps is located in a small size deep alluvial valley and faces important site effects lebrun et al 2001 in order to identify and quantify multidimensional site effects in this basin a very dense array of 29 three component seismometers over a 1 km aperture was installed within the city the wave field complexity as well as the in situ noise characteristics colored correlated noise and low signal to noise ratio led us to develop a procedure based on time frequency coherence of signal waveforms and the multiple signal classification music schmidt 1981 algorithm to identify the main energetic contributions crossing the array next the nature and energy of waves were estimated using some properties of the analytical three component covariance matrix careful methodological investigations were performed in order to better understand and quantify the effects of site constraints on the estimation of wave parameters with the music technique simulations outline the ability of array antennas first to handle difficult scenarios involving multiple nonstationnary and correlated propagating phases and second to estimate the polarization and energy of waves the velocity estimation is shown to be much more unstable than backazimuth estimation and a low signal to noise ratio introduces some variation in estimates finally considering the very large number of identified waves a statistical view of final estimates is suggested for improving the reliability of analysis in an accompanying article cornou et al 2003 we use this method to investigate the entire wave field of seismic events recorded by the array in order to isolate basin induced waves manuscript received 21 june 2002

dense array recordings in the san bernardino valley of landers big bear aftershocks basin surface waves moho reflections and three dimensional simulations abstract fourteen geos seismic recorders were deployed in the san bernardino valley to study the propagation of short period t 1 to 3 sec surface waves and moho reflections three dense arrays were used to determine the direction and speed of propagation of arrivals in the seismograms the seismograms for a shallow d 1 km m 4 9 aftershock of the big bear earthquake exhibit a very long duration 60 sec of sustained shaking at periods of about 2 sec array analysis indicates that these late arrivals are dominated by surface waves traveling in various directions across the valley some energy is arriving from a direction 180 from the epicenter and was apparently reflected from the edge of the valley opposite the source a close in aftershock 25 km depth 7 km displays substantial short period surface waves at deep soil sites a three dimensional 3d finite difference simulation produces synthetic seismograms with durations similar to those of the observed records for this event indicating the importance of s wave to surface wave conversion near the edge of the basin flat layered models severely underpredict the duration and spectral amplification of this deep soil site i show an example where the coda wave amplitude ratio at 1 to 2 hz between a deep soil and a rock site does not equal the s wave amplitude ratio because of the presence of surface waves in the coda of the deep soil site for one of the events studied 90 km there are sizable phases that are critically reflected from the moho pmp and sms at one of the rock sites the sms phase has a more peaked spectrum that the direct s wave

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

paleoweathering and depositional conditions in the inter flow sediment units bole beds of deccan volcanic province india a mineral magnetic approach abstract a total of 54 samples from thirteen different profiles of interflow sediment units occurring in the deccan volcanic province dvp india are studied using an integrated mineral magnetic and field documentation approach the occurrence and distribution of ferri and antiferromagnetic oxides associated with these sediments infer depositional conditions dominated by various detrital modes and recycling of baked sediments under limited authigenic environments the baking of underlying sediments is conditioned by aqueous or dry nature of the substrate vis a vis the viscosity of the overlying lava flow that can be identified by a combination of brown red boles and compact pahoehoe type flows the presence of antiferromagnetic superparamagnetic sp fraction in the red bole capped brown boles indicates the depth of baking to 20 cm while the sp fraction also marks infilling recycling and pigmentation in other occurrences of the red boles studied here overall the mixed magnetic mineralogy and sediment characters depict frequent recycling and re deposition by surface run off infiltration and ponding as the most common processes of bole bed formation in dvp governed by shallow streams or laterally migrating channels infiltration of the baked or unbaked sediments into fragmentary topped basalts is frequently shown by the red and brown boles while infilling into the interstices and cavities is common with green boles the red boles are also characteristic of detrital mixing of oxidized partially oxidized ferrimagnets many times coated with pigmentary hematites the present results envisage a great scope for the routine mineral magnetic studies integrated with field observations for rapid characterization of the extensively occurring bole bed horizons in the dvp and their study as analogs of martian soils and sediments

siwalik paleosols miocene northern pakistan genesis and controls on their formation abstract paleosols of the siwalik group upsection the chinji nagri and dhok pathan fms in northern pakistan are associated with fluvial and lacustrine deposits that accumulated adjacent to the rising himalayas there are two types of well developed paleosols throughout the sequence 1 noncalcareous bk paleosols are typically composed of a nodular calcite bk horizon overlain by a noncalcareous horizon noncalcareous horizons are characterized by the absence of matrix calcite and presence of iron oxide accumulations nodular calcite horizons are characterized by abundant large calcite nodules 2 calcareous paleosols are characterized by the presence of matrix calcite and lack of horizonation the two paleosol types reflect differences in drainage condition parent material topography and water table elevation most noncalcareous horizons formed under relatively well drained conditions on topographic highs the lack of matrix calcite in most cases is due to noncalcareous parent material however some noncalcareous horizons apparently developed in well drained topographic lows on noncalcareous and or subsequently leached calcareous substrates nodular calcite horizons formed within the capillary fringe the source of most of the calcite was groundwater however calcite nodule formation was largely dependent upon pedogenesis calcareous paleosols formed under relatively poorly drained conditions probably within the capillary fringe in topographic lows most matrix calcite was inherited from parent material both paleosol types formed i areas of little or no deposition other poorly developed paleosols represent incipient noncalcareous bk and calcareous paleosols and formed in areas of moderate deposition no soils formed in areas of high deposition cumulative and compound pedogenesis occurred locally cumulative pedogenesis was more common during deposition of the upper nagri and lower dhok pathan fms consistent with a documented increase in compacted sediment accumulation rates upsection features indicative of episodic wetting and drying including evidence of alternating calcite and iron oxide precipitation are consistent with previous paleoclimatic interpretations indicating that the regional climate from 15 ma to 9 ma was warm humid subtropical to tropical and markedly seasonal attributable to monsoonal c nditions

a double seismic antenna experiment at teide volcano existence of local seismicity and lack of evidences of volcanic tremor data analyzed in the present work correspond to a 40 days field experiment carried out in teide volcano canary islands spain with two short period small aperture dense seismic antennas in 1994 the objective of this experiment was to detect analyze and locate the local seismicity we analyzed also the background seismic noise to investigate the possible presence of volcanic tremor from a set of 76 events we selected 21 of them in base of their good signal to noise ratio and their possibility to locate their seismic source by using the seismic antennas a visual classification based on the s p time and seismogram shape has permitted to establish three groups of events local seismicity s p time between 3 and 5 s very local earthquakes s p time smaller than 3 s and artificial explosions these earthquakes have been located by applying the zero lag crosscorrelation technique and the inverse ray tracing procedure those earthquakes that were recorded simultaneously by both seismic antennas were also located by intersecting both back azimuths the analysis of the seismicity has revealed that the amount of seismicity in teide volcano is moderate this seismicity could be distributed in three main areas inside the caldera edifice below the teide pico viejo complex in the eastern border of the caldera edifice and offshore of the island at present this activity is the only indicator of the volcano dynamics the analysis of the back ground seismic noise has revealed that at frequencies lower than 2 hz the oceanic load signal is predominant over other signals even over local earthquakes with a magnitude of 2 0 due to this although if in the teide area were present a weak volcanic tremor or other volcanic signals with predominant peaks below 2 hz to observe them would be a very difficult task q 2000 elsevier science b v all rights reserved

subsalt 3d vsp imaging at deimos field in the deepwater gulf of mexico at deimos field in the deepwater gulf of mexico surface seismic imaging cannot fully image sedimentary structure near the steeply dipping base of salt 3d vertical seismic profile vsp imaging was introduced to the deepwater gom to improve seismic imaging of complex structural and stratigraphic features ray et al 2003 hornby et al 2006 and recently has been used for imaging blind spots in surface seismic coverage hornby et al 2005 hornby et al 2007 with this method 3d surveys are conducted using a surface source vessel and downhole geophones here we investigate the use of 3d vsp imaging to complement the surface results with additional coverage beyond that of the surface seismic adjacent to the complex salt body

distinguishing early groundwater alteration effects from pedogenesis in ancient alluvial basins examples from the palaeogene of southern portugal colour mottling and horizons of secondary carbonates are common in ancient alluvial sequences and are normally interpreted as pedogenic features they have been used to assess palaeoclimates soil drainage conditions and deposition rates palaeogene alluvial deposits in the sado and lisbon basins of portugal exhibit prominent colour variations and mottle patterns as well as carbonate accumulations both at the bases of fining upwards cyclothems and as thick units up to 20 m capping alluvial megasequences however these colour and carbonate features are interpreted as the products of shallow saline reducing groundwaters unrelated to pedogenesis such non pedogenic products are easily mistaken for soil formed ones and criteria for differentiating the two are reviewed to assist interpretations in other alluvial deposits key criteria are thickness gradational tops and bases absence of soil horizon features occurrence in coarser alluvium and prevalence of hydromorphic colour and mottling patterns

using magnetic susceptibility to facilitate more rapid reproducible and precise delineation of hydric soils in the midwestern usa abstract standard field indicators currently used for hydric soil delineations usda nrcs 1998 field indicators of hydric soils in the united states version 4 0 in g w hurt et al ed united states department of agriculture nrcs fort worth tx are useful but in some cases they can be subjective difficult to recognize or time consuming to assess magnetic susceptibility ms measurements acquired rapidly in the field with a portable meter have great potential to help soil scientists delineate and map areas of hydric soils more precisely and objectively at five sites in illinois from 5 to 15 ha in area with contrasting soil types and glacial histories the ms values of surface soils were measured along transects and afterwards mapped and contoured the ms values were found to be consistently higher in well drained soils and lower in hydric soils reflecting anaerobic deterioration of both detrital magnetite and soil formed ferrimagnetics at each site volumetric ms values were statistically compared to field indicators to determine a critical ms value for hydric soil delineation such critical values range between 22 10 5 and 33 10 5 si in silty loessal or alluvial soils in illinois but are as high as 61 10 5 si at a site with fine sandy soil a higher magnetite content and slower dissolution rate in sandy soils may explain the difference among sites with silty parent material the lowest critical value 22 10 5 si occurs in soil with low ph 4 5 5 5 since acidic conditions are less favorable to ferrimagnetic mineral neoformation and enhance magnetite dissolution because of their sensitivity to parent material properties and soil ph critical ms values must be determined on a site specific basis the ms of studied soil samples 0 5 cm depth is mainly controlled by neoformed ultrafine ferrimagnetics and detrital magnetite concentrations with a minor contribution from anthropogenic fly ash neoformed ferrimagnetics are present in all samples but based on high fd 5 to 10 are most prevalent in high ph mollisols of northeastern illinois scanning electron microscope images display significantly more detrital magnetite alteration in hydric soils substantiating that reductive dissolution of magnetite aided by microorganisms is a primary cause for lower ms fly ash comprises 8 50 of the 5 m strongly magnetic particles and typically accounts for 5 15 of the total ms signal the proportion of fly ash in 5 m strongly magnetic fractions is greater in hydric soils because of lower natural magnetite contents possibly combined with historical topsoil accumulation in lower landscapes magnetic fly ash particles are also more altered in low ms soils implying that significant magnetite dissolution can occur in less than 150 years

isotopic evidence for ecological and climate change in the richly fossiliferous plio pleistocene upper siwalik deposits exposed around chandigarh india abstract the plio pleistocene siwalik deposits around chandigarh well known for their great wealth of mammalian fossils preserve a continuous record of calcareous paleosols ranging in age from 2 7 to 0 6 ma the carbon isotope composition 13c relative to vienna peedee belemnite vpdb of 140 pedogenic carbonates from ghaggar and nadah sections and 13 gastropod samples from nadah section record a landscape primarily occupied by c4 grasses during this interval however a mixed c3 c4 vegetation between 2 15 and 1 7 ma and a progressive increase in the percentage of c3 plants from 1 1 to 0 6 ma has been recorded most of the pedogenic carbonate 18o values vpdb in the ghaggar river section range between 5 29 and 8 93 indicating the dominance of monsoon climate these 18o values exhibit somewhat consistent trend in relation to 13c values suggesting influence of climate on the vegetation at two instances 1 07 and 0 66 ma there is significant depletion in carbonate 18o and 13c values suggesting monsoon intensification and a synchronous development of c3 vegetation pedogenic carbonate and gastropod 18o values vpdb in the nadah paleoswamp also exhibit consistent trends in relation to 13c values indicating steady relationship between short term climatic fluctuations in terms of warm humid and cool dry conditions and the abundance of c3 c4 biomass on the landscape nearly 1 8 ma ago the vegetation change on the siwalik landscape during early and middle pleistocene appears to have been influenced mainly by the regional tectonics sedimentation patterns and monsoonal rains rather than global climate changes

coalescence megafan multistorey sandstone complex of the late orogenic mio pliocene sub himalayan belt dehra dun india in the himalayan foreland basin a prominent multistorey sandstone complex in the middle siwalik subgroup is exposed along the southern flank of the dehra dun valley in the mohand anticline extending laterally for 40 km the middle siwalik subgroup consists of sandstone mudstone couplets 300 450 m thick in the lower part and the multistorey sandstone complex 900 1200 m thick in the upper which forms a gross coarsening upward sequence the major lithofacies are trough cross stratified sandstone planar cross stratified sandstone ripple drift laminated sandstone horizontal laminated sandstone and massive sandstone with subordinate amounts 20 of mudstone and conglomerate the multistorey sandstone complex is punctuated by several erosional surfaces over which abundant mud clasts are present the trough cross stratification exhibits a dominantly southward palaeoflow with much variation in the southeast and southwest quadrants however at outcrop level the palaeoflow data reveal internal consistency this spatial and temporal variability in palaeoflow direction indicates the existence of two major drainage systems of coalescing alluvial megafan type the estimated palaeochannel sinuosity is of the order of 1 04 to 1 23 with a return period of 4 to 8 103 years palaeoflow variability facies distribution frequent avulsion and the coarsening upward sequence collectively suggest the progradation of coalescing alluvial fans towards the south and southwest this was principally controlled by thrust movements and differential basin subsidence at the margin of the himalayan orogen

rainfall dependent transformations of iron oxides in a tropical saprolite transect of hainan island south china spectral and magnetic measurements 1 the iron oxide content of soils and sediments controlled by weathering and pedogenesis is generally considered a reasonable indicator of climate previous studies in temperate zones have established a positive correlation in aerobic soils between ferrimagnets and low to moderate rainfall the correlation seems to be reversed under extreme climates with high rainfall here we present a transect of saprolitic soils from hainan island south china with high rainfall 1440 2020 mm yr little temperature variation 23 24 c and extreme weathering along this transect we observed that both hematite concentration and magnetic susceptibility decrease with increasing rainfall whereas goethite concentration displays a large increase however there is no systematic trend in the total amount of iron oxides related to chemical weathering intensity along the transect goethite is the favored mineral phase of iron oxide with increasing rainfall and accumulates at the expense of hematite and maghemite through the dominance of rainfall driven processes these pedogenic processes coincide with the fundamentals of previous nonmonotonic models of hematite magnetic susceptibility and rainfall control of an inflection point this study also verifies a common genetic relationship between hematite and pedogenic ferrimagnets across a wide climate range a conceptual model considering both rainfall and temperature is proposed to help interpret the mechanism of ferrimagnet formation and changes in the rainfall inflection point

climatic thresholds for pedogenic iron oxides under aerobic conditions processes and their significance in paleoclimate reconstruction abstract iron oxides are widely distributed across the surface of the earth as a result of the aerobic weathering of primary fe bearing minerals pedogenic iron oxides which consist mainly of hematite hm goethite gt maghemite mgh are often concentrated synchronously in aerobic soils under low to moderate rainfall regimes magnetic susceptibility and redness which respectively reflect the content of mgh and hm in soils are considered reasonable pedogenic and climatic indicators in soil taxonomy and paleorainfall reconstruction however under high rainfall regimes the grain growth of mgh and transformation to hm combined with the prior formation of gt under conditions of high relative humidity rh can result in magnetic reduction and dramatic yellowing of soils and sediments which explains the existence of rainfall thresholds for mgh and hm at a large scale even before the pedogenic environment turns anaerobic in order to capture the rainfall thresholds for mgh and hm occurring under aerobic conditions we explored a tropical transect across a granitic region where the soil color turned from red to yellow under a wide rainfall range of 900 2200 mm yr and a corresponding mean annual rh range of 77 85 we observed a lower rainfall threshold of 1500 mm yr and a corresponding rh 80 for mgh and hm along this transect as well as a higher rainfall threshold of 1700 mm yr and a corresponding rh of 81 for gt and total pedogenic iron oxides citrate bicarbonate dithionite extractable fe fe d cross referencing with comparable studies in temperate and subtropical regions we noted that the rainfall or rh thresholds for fe d and hm or mgh likewise increase with temperature moreover the different thresholds for total and individual iron oxide phase indicates that a negative correlation between chemical weathering intensity and redness or in sediment sequences can occur under the prevalent climate regime just between their thresholds finally we developed an integrated model to interpret the sequential formation of rainfall thresholds for different pedogenic iron oxides in soils and sediments with conditions from aerobic to anaerobic

lateral propagation effects observed at parkway new zealand a case history to compare 1d versus 2d site effects abstract the importance of 2d or 3d site effects has been shown by theoretical studies however there is a lack of observational evidence of site effects due to lateral heterogeneities we have evaluated 1d and 2d site effects in the data obtained by a dense seismograph array that operated for more than 2 months in the alluvial basin of parkway new zealand 1d site effects were evaluated using three independent techniques spectral ratios relative to a reference station spectral ratios of horizontal relative to vertical ground motion and a generalized inversion scheme site effects due to lateral heterogeneity were investigated in detail for two events using frequency wavenumber analysis our results show that it is not possible to separate 1d from 2d site effects using frequency domain techniques this explains the scatter obtained from standard 1d data analysis the 1d resonance peaks will be more or less contaminated with laterally propagating waves for different events

a conceptual model for the enhancement of magnetic susceptibility in soils abstract mineral magnetic properties of soils can be strongly influenced by soil forming factors understanding how climate influences magnetic transformations in soils may offer insight into paleoclimate and the pedologic history of landscapes based on our experience with soils in california and hawaii we have developed a conceptual model of the pathways that can lead to enhancement of the magnetic susceptibility in soils we base our model on three sources of iron in soils magnetite maghemite and other iron bearing minerals we find that preferential accumulation transformation diagenesis lessivage neoformation authigenesis and solubilization are the main processes that convert the primary lithogenic minerals inherited from soil parent material to the secondary pedogenic minerals found in the solum biosynthesis is included in the model but does not appear to be an important process in aerobic soil environments our model shows that a major process in the enhancement of eluvial and illuvial horizons is neoformation of secondary magnetite and maghemite resulting from precipitation of iron from the soil solution the processes and products in the model are independent of whether the parent material is transported alluvium or loess or residuum for the soils that we have studied the rates of susceptibility enhancement are shown to be dependent on climate and parent material

using the spac microtremor method to identify 2d effects and evaluate 1d shear wave velocity profile in valleys the requirement of a layered earth geology is a restrictive assumption when using the spatially averaged coherency spectra spac method numerical simulations of microtremors and spac observations recorded in the tamar paleoval ley launceston tasmania australia are used to assess the potential of the spac method to identify two dimensional 2d effects and evaluate one dimensional 1d shear wave velocity swv profile in a valley environment the tamar valley is approximately 250 m deep by 700 1000 m wide it is filled with soft sediments from the tertiary and quaternary periods above hard dolerite bedrock of jurassic age observed coherency spectra of the vertical component are analyzed at two sites in the tamar valley using two 50 m radius centered triangular arrays above the deepest point of the valley at site dbl and above the east flank of the valley at site rgb simulated and observed coherency spectra suggest the propagation of rayleigh waves of first higher mode at the sv frequency of resonance of the tamar valley affects the coherency spectra recorded with pairs of sensors perpendicular to the valley transverse coh simulated and observed coherency spectra recorded above the deepest point of the valley site dbl with pairs of sensors parallel to the valley axis axial coh are not affected by these edge generated rayleigh waves and agree well with the theoretical coherency spectrum computed from the preferred 1d swv profile the simulated and observed results from this paper suggest that differences between the observed axial coh and transverse coh give an indication of the exis tence of the 2d buried valley results also suggest that the observed coherency spectra recorded on pairs of sensors oriented parallel to the valley axis can provide a reliable evaluation of a 1d swv profile above the deepest point of a deep and narrow valley such as the tamar valley

deterministic frequency wavenumber methods and direct measurements of rupture propagation during earthquakes using a dense array data analysis data recorded by the smart 1 array in taiwan are used to make the first direct measurements of two dimensional earthquake rupture propagation using frequency wavenumber techniques and ray theory we obtain estimates of the spatial extent duration and directions of rupture propagation during two earthquakes located offshore taiwan our estimates include uncertainties due to errors in fault plane location and orientation velocity structure and slowness ray parameter measured at the array we find that the january 29 1981 ml 6 3 taiwan earthquake ruptured unilaterally updip and toward the west on a 60 dipping 109 striking reverse fault using p waves we find its fault length and duration to be 25 18 km and 7 4 3 4 s respectively s waves indicate a fault length and duration of 27 15 km and 9 4 3 6 s respectively we suggest that the november 14 1986 ml 7 0 hualien taiwan earthquake was triggered by a shallow h 14 km foreshock ml 5 4 which occurred on a subparallel or splay fault approximately 5 s before the mainshock based on p waves rupture propagation during the foreshock is unilateral towards the northeast and slightly downdip on a 58 dipping 38 striking reverse fault its spatial extent and duration are approximately 23 km and 5 4 s the mainshock initiated at greater depth h 34 km than the foreshock with its primary direction of rupture unilateral toward the northeast and slightly updip on a 57 dipping 43 striking reverse fault using p waves we found a spatial extent and duration of 68 15 km and 12 4 2 2 s s waves indicate a similar extent duration and direction of propagation for the mainshock however we found it difficult to distinguish the foreshock and mainshock 5 waves we show by example that these results represent an improvement over what can be obtained using long period t 5 s teleseismic methods comparison of our results with those obtained using teleseismic data suggests either a short duration slip time function or that most slip occurs near the rupture front our results indicate that much of the complexity in the seismograms recorded during these events by the smart 1 array is due to spatial and temporal variations of the source this suggests that at least in some cases predictions of both the phase and amplitude of strong ground motion as a function of time would require a priori knowledge of source properties finally we recommend siting small 10 station dense arrays on land above offshore subduction zones which are considered seismic gaps because they can provide more detailed measurements of rupture propagation than is presently possible

basin induced love waves observed using the strong motion array at fuchu japan phases have been observed in the s wave coda of local earthquakes recorded at the fuchu strong motion array located in the kanto basin in the western suburbs of tokyo japan these phases are often larger than the direct s wave at a period of 1 sec because these phases are observed only on horizontal components at surface sites and are weakly observed at only the shallowest 150 m of a number of borehole sites they are interpreted as love waves particle motions indicate significantly off azimuth travel directions the fuchu array is too sparse to allow the application of standard array analysis to determine the origin of these phases instead we use a combination of three component polarization enveloping and slant stack techniques that allows propagation directions to be reasonably well determined 10 however group slownesses are more difficult to obtain precisely 1 to 2 sec km using these results and assuming that the love waves are generated by the scattering of s waves at the earth s surface we estimate locations of scattering points we find that the scattering occurs along a short segment of the kanto basin boundary for widely distributed earthquake source locations we believe that this segment is important because it is the closest part of the basin boundary to the observation sites the existence of these basin induced love waves violates backscattering models for the generation of the coda of local earthquakes this must be kept in mind when applying coda techniques to sediment basin sites at periods of 1 sec or more

site effect study in urban area experimental results in grenoble france three methods are used to determine the site effect in the town of grenoble located in the western alps first we use the classical spectral ratio method in 14 sites to calculate the transfer function of the basin we find an amplification of 10 in the frequency range of 0 25 to 10 hz second we compare these results with the h over v spectral ratio method and propose a map of resonance frequency of the basin we find a lower resonance frequency in the center of the basin than on the edge that is consistent with the structure deduced from a gravity bouguer anomaly map finally we use the empirical green s function method to simulate a m w 5 5 earthquake at a distance of 20 km from the town the simulated acceleration reaches the level of 2 m s2 in the center of the basin compared to 0 2 m s2 on the edges the simulated ground motion we compute is smaller than the french seismic codes on the edge of the valley but significantly larger in the center

short baseline variations in site response and wave propagation effects and their structural causes four examples in and around the santa clara valley california abstract ground motion records of local and regional events from a portable array are used to investigate the structural causes of variations in ground motion over distances of a few hundred meters to a few kilometers in the sedimentary basin environment of the santa clara valley california and its margins arrays of portable seismic stations are used to target four study areas with different ground motion patterns 1 an edge of the alluvial basin extending up onto a marginal ridge blossom hill 2 a cenozoic basin with a nearly flat bottom cupertino basin 3 a long narrow cenozoic basin with a steep v profile evergreen basin and 4 a line perpendicular to the trace of the hayward fault average peak velocities on blossom hill from local earthquakes are a factor of 2 5 times higher than nearby valley sites three dimensional 3d modeling is used to conclude that the majority of the amplification is due to lower shear wave velocities along a local fault zone shannon berrocal site amplification over the cupertino basin in the frequency band 0 5 4 hz is generally low less than 2 0 relative to a mesozoic rock site and spatially uniform this response is attributed to the shallow flat bottomed shape of the basin and the uniform flat laying sedimentary fill in contrast site amplification in the evergreen basin generally exceeds 3 0 and is attributed to the deep v shaped geometry of the basin and younger sedimentary fill 3d waveform modeling shows the elongated shape of the evergreen basin causes more efficient trapping of long period waves for sources along the long axis of the basin a low velocity zone is postulated along the hayward fault with a width between 100 and 200 m based on elevated site response along the fault trace and 4 5 hz fault zone guided waves on the horizontal components of stations near the fault

seismic site characterization of an urban sedimentary basin livermore valley california site response basin edge induced surface waves and 3d simulations thirty two accelerometers were deployed in the livermore valley california for approximately one year to study sedimentary basin effects many local and near regional earthquakes were recorded including the 24 august 2014 m w 6 0 napa california earthquake the resulting ground motion data set is used to quantify the seismic response of the livermore basin a major structural depression in the california coast range province bounded by active faults site response is calculated by two methods the reference site spectral ratio method and a source site spectral inversion method longer period 1 s amplification factors follow the same general pattern as bouguer gravity anomaly contours site response spectra are inverted for shallow shear wave velocity profiles which are consistent with independent information frequency wavenumber analysis is used to analyze plane wave propagation across the livermore valley and to identify basin edge induced surface waves with back azimuths different from the source back azimuth finite element simulations in a 3d velocity model of the region illustrate the generation of basin edge induced surface waves and point out strips of elevated ground velocities along the margins of the basin online material figures comparing 5 damped acceleration response spectra for data and synthetics

analysis of three component ambient vibration array measurements summary both synthetic and observed ambient vibration array data are analysed using high resolution beam forming in addition to a classical analysis of the vertical component this paper presents results derived from processing horizontal components we analyse phase velocities of fundamental and higher mode rayleigh and love waves and particle motions ellipticity retrieved from h v spectral ratios a combined inversion with a genetic algorithm and a strategy for selecting possible model parameters allow us to define structural models explaining the data the results from synthetic data for simple models with one or two layers of sediments suggest that in most cases the number of layers has to be reduced to a few sediment strata to find the original structure generally reducing the number of soft sediment layers in the inversion process with genetic algorithms leads to a class of models that are less smooth they have a stronger impedance contrast between sediments and bedrock combining love and rayleigh wave dispersion curves with the ellipticity of the fundamental mode rayleigh waves has some advantages scatter is reduced when compared to using structural models obtained only from rayleigh wave phase velocity curves by adding information from love waves some structures can be excluded another possibility for constraining inversion results is to include supplementary geological or borehole information analysing radial components also can provide segments of rayleigh wave dispersion curves for modes not seen on the vertical component finally using ellipticity information allows us to confine the total depth of the soft sediments for real sites considerable variability in the measured phase velocity curves is observed this comes from lateral changes in the structure or seismic sources within the array constraining the inversion by combining love and rayleigh wave information can help reduce such problems frequency bands in which the rayleigh wave dispersion curves show considerable scatter are often better resolved by love waves information from the horizontal component can be used to correctly assign the mode number to the different phase velocity curve segments especially when two modes seem to merge at osculation points such merging of modes is usually observed for rayleigh waves and thus can be partly solved if additional information from the love waves and the horizontal component of rayleigh waves is considered whenever a site presents a velocity inversion below the top layer love wave data clearly helps to better constrain the solution

edge diffracted 1 sec surface waves observed in a small size intramountain basin colfiorito central italy during the umbria marche central italy seismic sequence a small aperture 200 m four station array was operating in the colfiorito plain a few kilometers away from the epicenters of the ml 5 6 and 5 8 mainshocks of 26 september 1997 the array was deployed approximately 500 m from the eastern edge of the basin we analyze the three component seismograms of 12 aftershocks in a magnitude range of 2 5 to 4 1 amplitudes of the horizontal components are systematically higher than those of the vertical component with an average horizontal to vertical spectral ratio of about 3 at 1 hz in this frequency band earthquake induced ground shaking is highly coherent across the array a 1 sec running window zero lag cross correlation algorithm is used to compute apparent velocity and backazimuth of coherent wave trains in the frequency band 0 5 to 2 hz apparent velocity and backazimuth show a different behavior in the first part of the seismograms compared to the late coda the largest amplitude waves that is s waves and early coda are characterized by low apparent velocities mostly between 400 and 1200 m sec this suggests that near the rock edge the most significant part of seismic energy propagates horizontally in the basin backazimuth of these low frequency coherent wavetrains never coincides with the array to source direction the predominant backazimuth is peaked around n110 corresponding to the nearest steep outcrop of the basin edge the observed 1 sec coherent wave trains are interpreted as locally generated surface waves that are persistently diffracted from the nearby basin edge as long as a significant level of seismic radiation is incident to the bedrock when the bedrock excitation decreases a much larger variability of both apparent velocity and backazimuth is observed suggesting that in the coda randomly scattered waves within the basin and late arrivals of deeper origin become more important multipathing from the source to the site as well as multipathing within the basin are therefore interpreted as the main causes of the observed long duration coherent low frequency basin shaking

lithofacies and palaeosol analysis of the middle and upper siwalik groups plio pleistocene haripur kolar section himachal pradesh india abstract the middle upper siwalik groups plio pleistocene are exposed at haripur kolar himachal pradesh india the succession is 2800 m thick and has been subdivided into unit m1 of the middle siwalik and four units u1 u4 of the upper siwalik group on the basis of facies associations and type and degree of development of palaeosols the available magnetostratigraphic ages for bases of units u1 u3 and u4 are 5 5 2 6 and 1 77 ma respectively the top of the section has been dated as 19 ka lithofacies association and palaeocurrent analysis indicates that the middle and upper siwalik groups were formed mainly by a basin transverse fluvial system two types of river systems which differ in their size can be documented in unit m1 unit u1 and unit u2 one trunk river system similar to the modern kosi and the other smaller river system which formed tributaries to the former the large rivers were mainly braided in nature the unit u3 and lower part of unit u4 were deposited in the piedmont depositional system mainly by small braided streams and the upper part of the unit u4 was deposited during a period of arid climate by sediment gravity flows integration of fluvial lithofacies and pedofacies helps to identify two fluvial depositional systems from the modern indo gangetic plains the lowland system involved deposition on alluvial megafans and interfan areas which resulted in sand rich and mud rich sequences with weekly developed soils the upland system allowed large tracts to act as high ground for thousands of years thereby giving rise to sandstone poor intervals with moderately to strongly developed soils occurrence of moderately to strongly developed soils was controlled by uplifting and tilting of large tectonic blocks without any relation to distance from the main channels rate of subsidence apparently controlled the occurrence of lowland and upland systems deposition of the unit m1 unit u1 and unit u2 took place under upland and lowland systems very similar to those identified from the modern indo gangetic plains the warm and humid climate between 5 3 and 2 6 ma led to the formation of red alfisols with calcrete nodules at places slightly cooler and drier climate starting at about 2 6 ma and approximately coinciding with the onset of global scale glaciation produced poorly developed yellow soil with common development of nodular calcretic horizon and calcitc material disseminated in the groundmass at ca 0 9 ma a probable significant change to still drier and cooler climate produced typical sediment gravity flows in the piedmont system that continued until at least up to 19 ka

a multistorey sandstone complex in the himalayan foreland basin nw himalaya india abstract ten parallel stratigraphic sections 1500 1800 m thick spread over an area of 400 km2 in dehra dun sub basin dsb of the himalayan foreland belt hfb were studied to understand the anatomy of one of the largest 900 1200 m thick fluviatile multistorey sandstone complexes msc of the world using fluvial geometry compositional data and magnetic fabrics over a magnetostratigraphically controlled master section the multistorey sandstone complex between 10 5 ma representing the middle siwalik sub group comprises of grey medium to fine grained lithic arenites to lithic greywacke and records tectonic and or climatic episodes three main facies associations are recognised sandstone mudstone sandstone and conglomerate sandstone that represent fluvial fan deposit palaeocurrent data show radial palaeoflow pattern with major palaeodrainage towards the southern quadrant the magnetic fabric studies suggest three major tectonic pulses the first pulse at 8 7 ma resulted in the development of major depocenter for the msc the second pulse at 7 65 ma enhanced the sedimentation and progradation while the third pulse at 6 5 ma records overlapping earlier fluvial fan by another coarse grained piedmont alluvial fan thrust movement in the northern fold belt basement lineaments and rate of basin subsidence controlled the lateral and vertical facies distribution and palaeodrainage the sedimentation pattern of the multistorey complex is characterised by mainly sheet flood deposits of laterally avulsing unconfined braided rivers and resembles to the modern megafan sedimentation in the ganga basin to the south

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

modeling three dimensional site response effects in the marina district basin san francisco california abstract loma prieta aftershock data recorded in the marina district of san francisco clearly show a large amplification in ground motion and a much longer duration of shaking relative to the response recorded at nearby rock sites for frequencies between 1 and 10 hz some of the amplification can be explained by the difference in impedance between the marina sites and the rock sites however 1d models underpredict the amplification in the range 1 to 3 hz and cannot account for the increased durations the available geologic information within the marina district indicates lateral variations in sediment thickness and composition our previous experience with modeling wave propagation in these types of basin environments has shown that these structures can greatly amplify and prolong the duration of the signals observed at sites within the basin in this study the seismic response of the marina basin is modeled with a 3d finite difference wave field simulation technique results from the numerical simulations at the basin sites indicate that the large amplitude arrivals following the direct s wave are surface waves traveling at relatively slow apparent velocities in general the surface waves contain the strongest recorded motions and produce the long duration of shaking observed at these sites in addition spectral ground motions from the 3d basin models do fairly well in reproducing the observed spectral amplification near 1 hz that is characteristic of the basin sites the simulation results suggest that focusing effects due to the geometry of the basin structure itself have a significant impact in determining the resonant periods at these basin sites

pedogenesis and paleoclimate interpretation of the magnetic susceptibility record of chinese loess paleosol sequences in the chinese loess paleosol sequences from luochuan haanxi province china variations in the magnetic susceptibility have been accepted as an excellent proxy for paleoclimate and the standard interpretation is that climatic processes have enhanced the magnetic susceptibility of the paleosols beyond the base line level of the loess by using mineral magnetic properties and a soil chemistry extraction procedure we show that most of the magnetic susceptibility signal in both the paleosols and the loess is due to pedogenesis in effect loess deposition and pedogenesis are competing processes at all times and the presence of a paleosol simply indicates that the latter process was predominant these results imply that any interpretation of the paleoclimate record of loess paleosol sequences must recognize the pedogenic nature of the magnetic susceptibility signal and that the focus of future research must be on the critical role of climate in the development of the paleosols

fluvial systems in the siwalik miocene and wyoming paleogene abstract the 3 km thick miocene siwalik group himalayan foredeep in northern pakistan and the 2 km thick paleogene fort union willwood formations bighorn basin in wyoming both preserve long records of fluvial deposition adjacent to rising mountain belts depositional environments and associated habitats change across large basins along with changing physiography and with the location of different river systems that may have varied greatly in patterns of channel deposition and the drainage of adjacent floodplain areas deposits exposed in these two basins provide very different records of shifting paleoenvironments and patterns of basin filling these differences reflect distinct patterns and scales of depositional environments the nature of the exposures and the types of sedimentologic studies that have been carried out in each basin the siwalik group fills a basin that extended at least 1000 km along its axis and 150 250 km away from the mountain front comparison of siwalik deposits and modern drainages in the himalayan foredeep suggests the ancient siwalik basin was filled by large rivers that deposited low gradient sediment fans covering areas on the order of 1000 km 2 and by smaller intrafan rivers with more poorly drained floodplains despite the scale of these river systems relative to siwalik exposures in pakistan transitions between different systems have been recognized deposits of coeval river systems in the siwalik basin show pronounced differences in alluvial architecture the character of overbank deposits and the abundance and taphonomy of organic remains in contrast the bighorn basin in wyoming is a relatively small intermontane foreland basin extending 200 km along its axis and about 80 km across bighorn basin strata were deposited by a river that flowed south to north along the basin axis and by smaller rivers that flowed transverse to the basin axis much of this basin is exposed and thus it is possible to reconstruct changing patterns of deposition and environments through time in more detail than in the siwalik basin these patterns indicate changes in basin wide drainage conditions and environments through time but there are also important differences among coeval strata upsection shifts in environments and vertebrate faunas within both the siwalik and bighorn basins may reflect tectonic or climatic forcing but this comparison emphasizes the importance of recognizing deposits from different contemporaneous river systems before inferring such large scale controls on paleoecological change through time

deriving wavefield characteristics and shear velocity profiles from two dimensional small aperture arrays analysis of ambient vibrations in a small size alluvial basin colfiorito italy we analyze the dispersion characteristics of ambient noise vibrations for this purpose two dimensional 2d seismic array data were acquired in four different sites in the colfiorito plain an alluvial intramountain basin that exhibits strong site effects assuming seismic noise being mainly composed of surface waves we derive one dimensional 1d shallow shear velocity profiles through the inversion of dispersion curves measured by frequency wavenumber f k methods the inverted shear wave velocity profiles are consistent with a priori information for those sites that can be approximated by 1d simple models in these cases the use of passive records of seismic vibrations can be a valuable tool for determining the shallow velocity profile if a detailed depiction of velocity structure is not required the theoretical dispersion curves for rayleigh and love waves were compared with the measured dispersion curves for vertical and horizontal components respectively this allows us to discuss qualitatively the composition of ambient vibrations outlining a large proportion of love waves in the noise wave field and the effects of higher modes we also use the single station method for investigating the origin of the horizontal to vertical h v peak in the plain of colfiorito in terms of ellipticity of the fundamental rayleigh mode

rock magnetic characterization of pedogenesis under high energy depositional conditions a case study from the mio pliocene siwalik fluvial sequence near dehra dun nw himalaya india abstract systematic rock magnetic studies accompanied by field investigations are presented for 51 pedogenic horizons from magnetostratigraphically constrained middle upper siwalik fluvial sequence 9 4 ma near dehra dun in the himalayan foreland basin hfb detailed sedimentologic studies infer predominantly proximal to distal alluvial fan setting with considerably high rate of sedimentation 55 cm ka paleosol profiles in the mohand rao mr section are commonly truncated by channel activity these paleosols display few rootlets diffused color contrast amongst variegated pedogenic horizons rare concretions intense gleying at places and frequent incursions by sand silt layers the mean mass specific magnetic susceptibility lf for pedogenic horizons is 0 95 10 8 m3 kg max 1 4 10 8 m3 kg min 0 5 10 8 m3 kg and the associated non pedogenic layers is 0 82 10 8 m3 kg max 1 2 10 8 m3 kg min 0 4 10 8 m3 kg the low frequency dependence of the susceptibility fd mean 2 and high coercivities bocr mean 425 mt of the pedogenic layers infer the absence of finer pedogenic superparamagnetic sp fraction that might have depleted during post depositional burial processes acquisition of isothermal remanent magnetization irm shows under saturation and gentle upward trend even at high applied fields 4000 mt advocating the predominance of hematite and goethite sympathetic variation in the total organic and inorganic carbon content with iron oxides stable under warm humid oxidative arid and cold restricted conditions confirm the sensitivity of the rock magnetic parameters to ambient climatic condition relative variations in goethite hematite and ferrimagnetic contents have been derived from ratios mainly based upon selective irm saturations and their coercivities these studies are validated by sandstone petrography and clay mineralogy for the same section however the variation in rock magnetic parameters shows a better amplification and allows relative quantification of the ambient climatic conditions the assemblage of iron oxides using the rock magnetic ratios of the pedogenic layers in these high energy conditions broadly infer the prevalence of semi humid to semi arid climate entirely during the late miocene to early pliocene period in the hfb with an increased seasonality during early pliocene the present approach envisages a great scope for quantitative database under the given setup of high energy conditions that are common in the mio pliocene hfb

contribution of dense array analysis to the identification and quantification of basin edge induced waves part ii application to grenoble basin french alps settled on a deep sediment filled valley the city of grenoble french alps faces important site effects large amplification and significant duration in crease of ground motion even for moderate size events in order to study multidi mensional site effects a very dense array composed of 29 three component seis mometers over a 1 km aperture was operated during spring 1999 in the center of the city a total of 18 events 6 local 4 regional and 8 teleseismic with an acceptable signal to noise ratio could be recorded over a 4 month period the complexity of the wave field and in situ seismic noise constraints led us to develop a procedure based on time frequency coherence and the multiple signal classification algorithm to iden tify and characterize wave arrivals cornou et al 2003 applying the procedure to the 18 records it is clearly indicated that ground motion inside the valley is domi nated by basin edge induced waves that carry 4 times more energy than the direct wave field regardless of the type of event considered in addition the basin induced wave field is composed of 60 rayleigh waves and 40 love waves when consid ering energy carried by the three components if one considers only the energy of horizontal components this proportion is 50 rayleigh waves and 50 love waves the diffraction phenomena are mostly constrained by the 3d structure of the basin regardless of the azimuth of the event a study of the relative contribution of 1d and 2d 3d effects on recorded ground motion suggests at least at frequencies below 1 hz that the difference between the standard spectral ratio and 1d transfer function or possibly the horizontal to vertical ratio receiver function and nakamura esti mates might be due mainly to laterally propagating waves

spectral amplification in a sediment filled valley exhibiting clear basin edge induced waves various site response estimates are presented for a linear array deployed in the coachella valley california during the 1992 landers big bear aftershock sequence this systematic comparison is unique in that the response of the site is clearly dominated by basin edge induced waves average sediment to bedrock spectral ratios for long s wave windows which include the basin edge induced waves exhibit amplification factors as high as 18 below 7 hz the deep basin structure which gives rise to the obvious multi dimensional effects produces a fundamental resonant peak that shifts between basin sites from 0 23 to 0 48 hz as the depth to bedrock changes above 0 6 hz where the largest amplifications occur the response is remarkably similar between sites and appears to be dominated by a near surface layer that is relatively uniform across the valley the apparent fundamental resonant frequency of this layer is between 0 8 and 1 hz sediment to bedrock spectral ratios computed using shorter windows that exclude the basin edge induced waves imply that the multi dimensional effects are significant only below 4 hz where they increase amplifications by an approximate factor of 2 spectral ratios computed using coda windows taken at twice the s wave travel time exhibit amplifications that are an average factor of 1 7 greater between 1 and 4 hz than those of the s wave estimates this discrepancy does not improve by taking coda windows later at four times the s wave travel time horizontal to vertical component s wave spectral ratios do not agree with the sediment to bedrock ratios however they do exhibit a clear peak at the fundamental resonant frequency of the deep basin structure sediment to bedrock spectral ratios of ambient seismic noise are also inconsistent with the s wave estimates however horizontal to vertical noise ratios exhibit clear peaks near the fundamental resonant frequencies of both the deep basin structure below 0 6 hz and the suspected near surface layer between 0 8 and 1 hz therefore ambient noise data appear to provide valuable constraints on the basin structure ongoing efforts involve multi dimensional modeling of the observed basin edge induced phases and resonant frequencies

climatic interpretation of the luochuan and lingtai loess sections china based on changing iron oxide mineralogy and magnetic susceptibility abstract hematite and goethite estimated from diffuse reflectance spectra and magnetic susceptibility ms have been determined from both the luochuan and lingtai loess sections of the loess plateau of central china changing concentrations of these iron oxides and ms were used to determine paleoclimatic change based on a model that relates pedogenic production of hematite and magnetite to precipitation we propose two precipitation phases on the loess plateau during the last 2 6 ma from the wucheng red clay boundary up to paleosol s5 mis 13 precipitation on the loess plateau was moderate probably not frequently exceeding 450 mm yr and highly seasonal from s5 to the present precipitation during interglacial times has gradually increased to the present levels of 600 650 mm yr for the localities examined throughout the pleistocene spanning both glacial and interglacial conditions hematite to goethite ratios display a consistent decrease this decrease suggests that precipitation on the loess plateau has been getting less seasonal and or has been occurring during times when temperature was lower in addition to these long term changes it also appears that iron oxide records from the loess plateau exhibit 400 500 ka cycles from the wucheng red clay boundary to s5 these 400 500 ka cycles may be analogous to similar length cycles recorded in 13 c marine records in the south china sea and may be linked through weathering and silica production as a result of the asian monsoon

structure of the chamba nappe and position of the main central thrust in kashmir himalaya abstract the chamba nappe composed of an approximately 8 km thick sequence of late precambrian to jurassic age rocks is located between the higher himalaya crystallines hhc and the lesser himalayan lh formations of panjal imbricate zone piz in the kashmir himalaya to the south the panjal thrust demarcating the base brings the chamba nappe rocks over the panjal imbricate zone to the north the chamba nappe rocks lie over the metamorphic hhc along the south dipping chenab normal fault cnb a pervasive stretching lineation defined by a mineral lineation stretched pebbles and felspar phenocrysts plunges ne nne and occurs on the foliation cleavage surface this lineation is related to southward displacement of the chamba nappe the chamba nappe is folded by regional scale fold viz the chamba tandi and bharmor synclines and the tisa anticline these nw se trending folds structures were developed synchronously with southward thrusting of the chamba nappe the chamba nappe results from southwestward sliding of cover rocks from their basement hhc due to topographic uplift the main central thrust mct in kashmir himalaya is different from that of the kumaun and nepal himalaya the mct vaikrita thrust does not extend west of the beas river but it is exposed in the rampur window and the kishtwar window separating the hhc from the underlying lh rocks southward propagation of the mct from the window zone up cutting the overlying hhc is transferred to the panjal thrust which transports the chamba nappe to the south over the lesser himalayan formations

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

evidence for the dissolution of magnetite in recent scottish peats abstract magnetic hydrological and geochemical data for 11 scottish peat cores confirm previous reports that anthropogenic pollutants constitute the principal source of ferrimagnets to such environments but indicate that postdepositional fe3o4 persistence may be more limited than formerly envisaged in all cores the lower stratigraphic limit of magnetic enrichment coincides with the water table below which negative mv values and enhanced ratios of fe mn and cu zn depict an abrupt transition to a strongly anoxic regime dissolution of fe3o4 in the reducing inundated zone is also signified by the more rapid down core loss of magnetic properties in cores from topographically depressed sphagnum lawns than in those from more elevated calluna hummocks as a consequence the peak and cumulative sirm values for cores from the former settings appear disproportionately low and the magnetostratigraphic records from adjacent but topographically variant sites are frequently asynchronous in contrast to most marine and lacustrine sediments dissolution of fe3o4 in peat induces a refinement of magnetic mineral assemblages highlighted by declining sirm arm ratios with depth and a hardening of remanence near the base of the magnetically enhanced strata sem micrographs of magnetic extracts from one scottish core indicate that this refinement results from preferential dissolution along crystallographic weaknesses within multidomain phases ultimately causing their disintegration and the adoption of single domain type magnetic behavior rates of dissolution are considerably greater than those reported for marine sediments probably due to the unusually high dissolved sulfide concentrations in mire waters

tectonic impact on the fluvial deposits of plio pleistocene himalayan foreland basin india abstract the himalayan foreland basin comprises a number of subbasins developed in various sedimentary environments during the plio pleistocene phases of himalayan orogeny this paper describes the evolutionary processes that led to the development of the himalayan foreland basin in the dehra dun and subathu subbasins the dehra dun subbasin essentially consists of conglomerate facies whereas subathu subbasin is primarily composed of sandstone mudstone intercalated with conglomerate the two subbasins were sites of braided river systems evidence from chronostratigraphy provenance and tectonic and climatic conditions suggests that differential tectonic movement sedimentation rate and basin subsidence coupled with climatic variation were responsible for the contrasting fluvial facies in these subbasins following the merger of the two subbasins at about 5 23 ma the conglomerate facies assemblage of the dehra dun subbasin passes laterally into a sandstone mudstone conglomerate facies assemblage of the subathu subbasin thickly bedded amalgamated sheet conglomerate of dehra dun subbasin has a high sedimentation rate 0 70 mm year between 5 23 and 4 8 ma with a slow rate of basin subsidence in contrast a slow sedimentation rate 0 39 mm year in coeval sediments of the subathu subbasin with relatively fast subsidence produced a succession of thick multistorey sandstone body with mature paleosols petrographic and clast composition data from dehra dun subbasin suggest that the detritus was derived from the pre tertiary lesser himalayan sequence lying in the north during an active tectonic phase of the main boundary thrust between 4 8 and 1 77 ma progradation of posttectonic conglomerate of the dehra dun subbasin continued during a quiescent phase of the main boundary thrust however as a consequence of partitioning of subathu subbasin along the intra foreland thrust interfingering of buff piedmont drainage and grey trunk drainage sandstones took place in contrast the syntectonic conglomerate of subathu subbasin originated from the uplifted proximal part of the foreland basin tertiary belt during the active phase of intra foreland thrust around 1 77 ma

interrelation of magnetic susceptibility soil color and elemental mobility in the pliocene pleistocene siwalik paleosol sequences of the nw himalaya india abstract apart from imparting color characteristics the precipitation and dissolution of fe oxides and hydroxides during pedogenesis is coeval with transformation and translocation of major and trace elements based on rock magnetic and geochemical parameters for 27 paleosol profiles from three stratigraphic columns of pliocene pleistocene siwalik sequence in the nw himalaya we describe here the relationship amongst elemental mobility munsell color and low field mass normalized magnetic susceptibility lf the study shows a consistent positive correlation of the rock magnetic parameters principally magnetic susceptibility with munsell hue and redness rating rr index torrent et al 1980 blavet et al 2000 of the soil profiles the late miocene profiles show an increase of 29 of al 2 o 3 concentration and that for the pliocene and pleistocene profiles show 33 to 60 increase as a result of pedogenesis similarly the other immobile elemental oxide fe 2 o 3 is increased by 54 in the late miocene profiles and 50 to 63 in the pliocene pleistocene profiles geochemical trends correlate with the lf showing r 2 0 39 to 0 68 with al 2 o 3 and fe 2 o 3 and r 2 0 40 to 0 73 for sio 2 similarly the munsell color parameters especially the rr index display significant positive correlation where the magnetic mineralogy is dominated by hematite and goethite these first order relationships amongst lf rr index and elemental mobility demonstrate the potential use of magnetic susceptibility for rapid characterization of the widespread and heterogeneous pedogenic episodes within the dynamic sedimentary environments of the himalayan foreland basin

shallow velocity structure and site effects at mt vesuvius italy from hvsr and array measurements of ambient vibrations abstract ambient vibrations were recorded by two dense short period seismic arrays located on mount vesuvius the aim of this study is to derive the surface velocity structure through the application of array techniques and to interpret it in terms of resonance effects mount vesuvius which is located in proximity to the apennines earthquake source zone is one of the most dangerous volcanoes of the world we compared different array techniques to derive the dispersive properties of the surface waves composing the noise wave field the frequency wavenumber f k spectral method applied to the data recorded by array a furnished the rayleigh waves and love waves dispersive functions and proved the time space stationarity of the noise wave field the existence of a stochastic wave field justifies the use of the spatial autocorrelation spac method and the time stationarity autocorrelation tsac method which appear to be most effective at the lowest frequencies the tsac method which time averages is confirmed as the most user friendly because it does not require circular geometries the knowledge of the surface structure is an important goal in site effects studies and is used to determine the frequency response of the near surface geology velocity models have been derived from the dispersion curves using both trial and standard inversion procedure the results are compared with those obtained from array measurements in adjacent areas scarpa et al 2003 revealing similar mechanical properties in the cover deposits and heterogeneities down to 40 m of depth the shear wave velocity profiles derived at the array sites are used to model the 1d transfer functions for vertically incident shear waves the fundamental resonance frequencies agree with the peak frequencies observed in the microtremor horizontal to vertical spectral ratios the frequency band of amplification is also compatible with the results obtained from local earthquakes at sites located at the same elevation on mount vesuvius galluzzo et al 2009

sedimentology of plio pleistocene late orogenic deposits associated with intraplate subduction the upper siwalik subgroup of a part of panjab sub himalaya india abstract this study provides a detailed sedimentologic documentation of the lithofacies cyclicity sandbody geometry palaeoflow variability and depositional models of the youngest late orogenic deposits of the siwalik molasse these deposits represent one of the important examples of sedimentation in the zone of intraplate subduction of the himalayan collision belt lithofacies analysis has resulted in the recognition of four conglomerate facies massive matrix supported conglomerate crudely stratified conglomerate trough cross stratified conglomerate planar cross stratified conglomerate five sandstone facies erosional scour and fill pebbly sandstone medium to coarse grained sandstone fine to medium grained ripple drift laminated sandstone bioturbated calcareous fine grained sandstone and six mudstone facies parallel laminated bioturbated mudstone reddish brown massive mudstone variegated mudstone bluish grey to violet mudstone buff coloured mudstone pebbly mudstone in addition hard calcareous layers have been recognised as a separate facies state the deduced cyclic sequences of the tatrot and pinjor formations of the upper siwalik subgroup show fining upward characters from cs coarse sandstone to ms mudstone through fs fine sandstone and ss alternations of sandstone and siltstone the sandbodies of the tatrot and pinjor formations reveal a sheet like geometry and an internal dominance of inter storey scour surfaces the presence of intraformational debris mud drapes reactivation surfaces and a general fining upward of grain size indicates fluctuating hydrodynamic conditions with frequent channel abandonment and re occupation resulting in net vertical aggradation the dominant style of sedimentation both in the channel and overbank facies is through vertical aggradation data on the palaeoflow variability indicates that the upper siwalik subgroup can be subdivided into four and three sediment vector sequences in the khetpurali and ghaggar sections respectively the palaeodrainage pattern in the khetpurali section reveals a major influence of northerly drainage twice in the stratigraphic column the high percentage of overbank deposits in individual cycles the lack of vegetal debris organic poor palaeosol units and abundant syngenetic caco 3 activity warrant comparison with the modern anastomosed deposits described from arid central australia some intervals of the sequences are comparable to the sublinear subparallel drainages with local anastomosis of the modern piedmont zone of the himalaya the higher parts of the stratigraphic column indicate proximal braided stream deposits and finally proximal alluvial fan deposits syntectonic activity has controlled the deposition of the megasequences which are a response to episodicity in the activity of basin margin basin margin or basin margin intrabasin structures the vertical stacking of the siwalik megasequences appears to be episodic in character

magnetic susceptibility of soils in different slope positions in saskatchewan canada abstract the magnetic susceptibility of soils varies with the slope position due to some factors such as texture and drainage class this study attempts to link to soil profile characteristics soil horizon type organic and inorganic c sand and oxalate feo and dithionite fed extractable iron measured on soil cores collected from the three uncultivated soil catenas in saskatchewan the parent material at all sites consisted of medium textured hummocky glacial till the waitville catena gray luvisol was developed under trees the weyburn catena dark brown chernozem under grass and the oxbow catena black chernozem had trees on the lower slope and grass in the center of the depression and on the upper and middle slopes in all the three catenas a downslope decrease in was correlated with increasing feo fed ratios and decreasing sand content lower slope gleyed profiles in the two chernozemic catenas had high feo fed ratios and low the impact of gleying was most evident in the solum and tended to increase in the c horizons of these profiles the of the sand and silt fractions was positively correlated with that of the bulk soil whereas the of the clay fraction did not vary with the of the bulk soil stable sand sized magnetite grains are believed to be rare in these soils

staining algorithm for seismic modeling and migration abstractin seismic migration some structures such as those in subsalt shadow zones are not imaged well the signal in these areas may be even weaker than the artifacts elsewhere we evaluated a method to significantly improve the signal to noise ratio s n in poorly illuminated areas of the model we constructed a phantom wavefield an extension of the wavefield to the complex domain the imaginary wavefield was synchronized with the real wavefield but it contained only the events relevant to a target region of the model which was specified using a staining algorithm the real wavefield interacted with the entire model however all structures except for the target were transparent to the imaginary wavefield which is excited only when the real wavefront arrives at the target structure the real and the imaginary source wavefields were crosscorrelated with the regular receiver wavefield the results were revealed in two images the conventional reverse time migration image and an image of the target

wavefield decomposition using ml probabilities in modelling single site 3 component records summary this paper presents a new approach to the analysis of three component digital seismograms earlier approaches used techniques such as principal components to estimate particlemotion using models of p and s waves in this paper the maximum likelihood ml estimator is preferred because this allows the use of x2 probabilities to test whether energy of a specific wave type p s love or rayleigh is present in addition this analysis allows the joint estimation of azimuth of approach and in cases of p and sv waves also apparent angle of incidence and hence information on apparent velocity for a single three component seismogram the covariance matrix provides only six independent observations thus restricting analysis to rather simple wave models the technique works satisfactorily for p waves whereas shear and surface wave models sometimes prove cumbersome to handle due to correlation between radial and transverse components reflecting complex propagation characteristics in inhomogeneous media this technique has been tested on synthetic data and in such cases works perfectly for all wave types an important aspect of this work has been the visual display of the probability and velocity information as functions of time and azimuth displaying the data in this form provides information on the ray path in a manner similar to analysis performed by seismic arrays practical examples on a variety of siesmic data are given to illustrate the viability of the technique the data cover a broad spectrum of frequencies and applications from broad band teleseismic data 1 hz regional seismic data 10 40 hz seismic profiling data 125 hz and vsp 500 hz recordings