seismic microzonation based on large geotechnical database application to lisbon abstract historically portugal has suffered the effects of several strong earthquakes in particular lisbon and the south and southwestern portuguese coast were affected by the largest known european earthquake on november 1st 1755 it is well known that the local ground conditions strongly affect the seismic ground motion modifying the signal s amplitude duration and frequency content which induces large variability in the motion induced to buildings and infrastructures aware of this situation the lisbon municipality promoted the development of a project to elaborate a new seismic microzonation map based on a large geotechnical database and geological data the eurocode 8 ground classification based on the vs30 parameter was adopted as reference however the geotechnical database has a very small number of geophysical logs and is mainly composed of borehole data and spt blows number an expedited methodology was applied to determine the n30 parameter as a proxy of the vs30 parameter non invasive field experiments surface waves seismic profiles and hvsr performed with ambient vibrations and data collected from independent geophysical reports were also used to check and validate the classification based on n30 because the distribution of the classified profiles was not uniformly distributed the final microzonation map was obtained from the combination of the profile classification and the surface geology

the accuracy of the low degree geopotential implications for ocean dynamics the low degree portion of a number of recent global gravitational fields have been tested for accuracy using precise accelerations measured on 24 hour satellites these measurements are independent of the data in the field models the results show that the most accurate of the recent solutions have degree error variances significantly less than 100 mm geoid height equivalent for all degrees less than five the broad and lasting features of ocean circulation should now be visible when comparing the geoid computed from this model with the average sea surface computed from satellite altimetry however before accurate mapping is possible the equivalent accuracy of the mean altimetric surface at long wavelengths needs to be verified

hydrographic conditions in the eastern pacific before during and after the 1982 83 el nino abstract between june 1981 and june 1984 a total of thirteen ctd sections were made across the equator along 85 w on some of these cruises additional sections were made along 5 s and 10 30 s between 85 w and the south american coast this sampling period covers the events that took place during the 1982 83 el nino these sections are used to describe the variability that took place before during and after this major event at the surface little evidence was found for a major southward flooding of warm low salinity water from north of the equator that has been observed during some previous el ninos major changes took place in the sub surface hydrographic structures the thermostad between 13 c and 16 c which is a prominent feature of the hydrography in this region disappeared early in 1983 and reappeared early in 1984 the vertical temperature gradient along the equator and along the coast which is usually quite variable with depth became much more uniform in early 1983 it regained its normal structure by early 1984 changes were not confined to the upper ocean but were evident over the whole depth interval sampled 1000m during november 1982 evidence was found for symmetric poleward spreading of the equatorial disturbance along the eastern boundary many of the changes that took place are consistent with linear models based on equatorial wave theory these observations presented a unique opportunity for observing the ocean response to a major interannual change in the wind forcing

lake gauge evidence for regional postglacial tilting in southern manitoba the network of lake level gauges in place for lake winnipeg lake winnipegosis lake manitoba and lake of the woods presents an opportunity to study the contemporary pattern of postglacial rebound in a north american continental interior region we used a regional trend surface model based on mean winter season differences of lake level between pairs of gauges to extract the postglacial rebound signature recorded in the lake gauge data the results from a best fitting planar model indicate that tilting is up to the northeast with a bearing of n 42 7 11 8 e and a rate of 10 7 2 2 10 9 rad yr 1 in spite of the fact that both the ice 3g and ice 4g load models are derived from the inversion of relative sea level histories obtained from marine coastal sites the pattern of rebound that we computed from these two ice models for this continental interior region agrees reasonably well with the pattern derived from the lake gauge data rates computed from an ice 3g load are in close agreement with those computed from the lake gauges whereas rates derived from ice 4g are 50 too slow when the planar pattern of postglacial rebound derived from the lake gauges in southern manitoba and lake of the woods is linked to the lake gauge derived pattern of rebound over the great lakes region the two region pattern suggests influential source regions of rebound that include southern and southwestern hudson bay as well as more local sources in western ontario it is possible that the spatial arrangement of ice domes predicted in the multidomed paleotopography of ice 4g could explain the two region pattern of rebound if more ice were added to ontario in the model or if earth structure assumptions could be modified or both as postglacial tilting continues to shift the region9s lakes to the southwest there is an increased risk of flooding and wave erosion along the south shores over the long term in addition postglacial tilting deforms the datums to which the lake level gauges are referenced thus where and how the levels of these lakes are measured is an important operational issue these factors present challenges to water resource managers who are responsible for monitoring the levels and controlling the outflows of these lakes

an intensity survey of households affected by the northridge california earthquake of 17 january 1994 following the northridge california earthquake of 17 january 1994 the humboldt earthquake education center heec conducted a telephone survey of approximately 6000 adults from within the felt region to study the earthquake s effects on individual households we tabulate human responses to the earthquake and observations of the earthquake s effects on inanimate objects from the heec survey as a function of independently assigned u s geological survey modified mercalli usgs mm intensity for the same communities human responses and subjective judgments about the severity of shaking when averaged over a large number of samples are useful discriminants of the levels of strong ground motion up to those associated with usgs mm intensity vii notwithstanding that individual human responses and subjective judgments are notoriously unreliable a threshold of strong ground motion corresponds to usgs mm intensity of about vii above which over 40 of respondents described the earthquake as violent and most people reported difficulty standing furniture displaced and some damage to their homes even at intensities viii and ix however relatively few people about 15 described their reaction as panic and only about 12 reported major damage to their homes the heec phone survey data show that in communities of low to moderate shaking usgs mm intensities estimated from a single postal questionnaire are quite robust at usgs mm intensity of v and below 88 of usgs mm intensities determined from postal questionnaires are within one intensity unit of intensities determined from the more numerous heec telephone survey data for the same community we introduce the concept of a community decimal intensity scale cdi based on telephone survey data and calibrated to agree on average with the usgs mm intensities the cdis are more regularly distributed than the usgs mm intensities and show much less scatter when plotted as a function of epicentral distance cdis show promise as a tool for comparing regional attenuation for delineating variations in shaking strength within areas mapped as a single mm zone and for rapid preliminary intensity estimates utilizing electronic media

topography at the core mantle boundary analysis of the earth s gravity field using ratio of gravity to geoid g n and cumulative degree contribution curve techniques improves resolution of the mass depth and dimensions of anomalous mass sources within the planet the source for four of the ten major geoid anomalies of the earth has large contributions from harmonic degrees 2 and 3 lie at the core mantle boundary and the greatest has a mass anomaly of 4 2 1022 grams that boundary has a density contrast 4 4 gm cm which is greater than at any other location including the contrast at the earth s surface with space thus relatively small vertical undulations of that boundary produce very large mass anomalies topographic relief of less than 3 km at the core mantle boundary occurs and accounts for the existence of the largest geoid anomalies occurring on the earth

gravity field determination and characteristics retrospective and prospective gravimetry has had a long history using pendulums torsion balances and static spring gravimeters relative accuracy adequate for many geophysical problems was already attained by 1900 but it took another half century to build readily portable gravimeters calibration and datum definition remained problems until the 1970s when free fall absolute gravimeters were developed that now have a precision of 10 3 mgal the problems of geographic inaccessibility and field party costs notably in areas of greatest tectonic interest are now being overcome by airborne gravimetry that has already achieved accuracies of 1 3 mgal with resolutions of 10 to 20 km satellite techniques are the best way to determine the long wavelength variations of the gravity field the resolution of the models has steadily improved with the number of satellites and the precision of the observations the best current model includes tracking data from more than 30 satellites satellite altimetry and surface gravimetry and has a resolution of about 290 km harmonic degree 70 with the most recent improvements coming from doppler orbitography and radiopositioning integrated by satellite doris tracking of the spot 2 satellite and satellite laser ranging slr doris and global positioning system gps tracking of the topex poseidon satellite meanwhile radar altimetry has become the dominant technique to infer the marine geoid with a resolution of tens of kilometers or shorter similarly the gravity fields of the moon venus and mars have been determined to harmonic degrees 70 75 and 50 respectively although tracking limitations result in variations of spatial resolution modeling earth s gravity field from the abundance of precise data has become an increasingly complex task with which the development of computer capacity has kept pace contemporary solutions now entail about 10 000 parameters half of them for effects other than the fixed gravity field of earth temporal variations arising from tides have long been well modeled and nontidal changes are now being identified the improvement in gravitational models engendered corresponding advances in geophysical interpretation isostatic models were refined and expanded to account for regional thermal and tectonic histories interpretation of the long wavelength gravity field determined by satellite techniques has been mainly in terms of plate tectonics as a manifestation of mantle convection gravity has been significant in inferring that there must be a large increase in viscosity with depth most strongly from the apparent slow sinking of subducted slabs the prospects for increasing accuracy and resolution in the determination of earth s gravity field rest primarily with the development of new measurement systems airborne gravimetry is taking promising new steps using gps but significant global model improvement awaits a dedicated satellite gravimetry system and future satellite altimeter missions will do more for ocean dynamics studies than geoid improvement advances in interpretation will occur through the development of other data such as seismic tomography and larger scale computer modeling of tectonics and convection

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

seismic property characterization of lithotypes cropping out in the siracusa urban area italy the town of siracusa is located in the south eastern coast of sicily southern italy in a wide inlet engraved into a limestone formation this lithotype which is overlaid by soft sediments such as sandy clays and detritus can be considered as the local bedrock present study aims to investigate on the dynamic properties of main lithotypes outcropping in the study area and their relationships with the local seismic response non invasive seismic prospecting techniques using the vertical component of surface waves masw and remi were adopted as well as ambient noise measurements processed through the nakamura technique the best solution for the experimental dispersion curves was selected using the neighbourhood algorithm and information about the deeper part of the estimated shear wave profiles was obtained by considering the ellipticity of the fundamental peak moreover a cluster analysis was performed to subdivide into homogeneous groups the experimental noise spectral ratios results obtained pointed out that the use of combined different methods provides a robust way to characterize the investigated soils and to reduce the problems linked to the non uniqueness of solutions during the interpretation of geophysical data

present day tilting of the great lakes region based on water level gauges by using monthly mean water levels at 55 sites around the great lakes a regional model of vertical crustal motion was computed for the region in comparison with previous similar studies over the great lakes 15 additional gauge sites data from all seasons instead of the 4 summer months and 8 additional years of data were used all monthly water levels available between 1860 and 2000 as published by the u s national ocean survey and the canadian hydrographic service were used for each lake basin the vertical velocities of the gauge sites relative to each other were simultaneously computed using the least squares adjustment technique our algorithm solves for and removes a monthly bias common to all sites as well as site specific biases it also properly weighs the input water levels resulting in a realistic estimation of the uncertainties in tilting parameters the relative velocities obtained for each lake were then combined to obtain relative velocities over the entire great lakes region finally the gradient of the relative rates for the regional model was found to agree best with the ice 3g global isostatic model of tushingham and peltier whereas the ice 4g gradients were too small around the great lakes

lageos scientific results introduction the lageos spacecraft is unique in that both its design and orbital characteristics were specifically chosen for high resolution geodynamic studies using satellite laser ranging techniques since its launch in 1976 the precision of single shot ranging observations made on the satellite has improved from several decimeters to a few centimeters with this level of precision it is possible to use lageos data for studies of contemporary plate movement polar motion gravity earth rotation and earth and ocean tides inferences about mantle structure and dynamics angular momentum coupling between the earth and its atmosphere and perturbative effects acting on earth satellites are being extracted from the data this special issue of the journal of geophysical research presents the current research results derived from lageos data

venus gravity a harmonic analysis an improved model of venusian global gravity has been obtained by fitting an eighteenth degree and eighteenth order spherical harmonic series to 78 orbital arcs of high altitude 950 1350 km at periapsis tracking data and 351 orbital arcs of lower altitude 150 200 km at periapsis data from the pioneer venus orbiter pvo compared to a recently published tenth degree model mottinger et al 1985 which is based on the 78 high altitude arcs only the current model provides a significant improvement in resolution and fidelity as a measure of this improvement we note that for the low altitude arcs alone the variance of the residuals for the present model is reduced to 19 of the data variance compared to 51 for the tenth degree model venus differs significantly from the earth in that it exhibits a significant correlation between long wavelength topography and gravity the gravity topography spectral admittances are inconsistent with either airy or pratt isostasy but they are consistent with dynamic support by mantle convection

status of the geopotential substantial progress has been made in modeling the geopotential field since the last reporting period anderle 1979a models of the gravity potential show improvement across the entire gravitational spectrum with resolution down to 1 haif wavelength major sources of data utilized for advancing our knowledge of the geopotential field consist of satellite laser ranging smith 1982 wilson 1979 linder 1981 which contributed to the long wavelength portion of the spectrum satellite altimetry geos 3 1979 seasat 1981 and improved surface gravity anomalies rapp 1981b both of which contributed to the intermediate and short wavelength features of the spectrum uniform global distribution of data in combination solutions is generally achieved by using altimeter data over the ocean and terrestrial gravity anomalies over land

hypsometry and relief analysis of the southern termination of the calabrian arc ne sicily southern italy abstract tectonic forcing causes the relief building of mountain chains and enforces the surficial processes in a persistent dismantling of rock volumes continuously modelling earth s surface actually we observe transient landscapes that have temporarily recorded tectonic forcing as a codified signal the late quaternary tectonic evolution of northeastern sicily located along the nubia eurasia plate boundary at the southern termination of the calabrian arc has been dominated by intense plio pleistocene dynamics that severely modified the late miocene landscape the present work aims to investigate geomorphically northeastern sicily essentially focusing on the hypsometric and relief analyses of the region in order to define how the topography responds to the post pliocene tectonic deformation we apply different relief morphometric indices hypsometric integral topographic relief and topographic dissection measured for each differently sized moving window and we use different swath topographic profiles as well our analysis evidences differential morphological responses between distinct morphotectonic domains of the studied area led by the combination of earlier morphological background and late quaternary tectonic deformation stages of the region in addition in the context of a constant and uniform tectonic uplift the results define the general space and time relating pathways of the landscape geomorphic metrics this enables us to bring out the controls of the vertical scale of landscape on hypsometry exploring their mutual relationships finally we reconstruct the late quaternary morphotectonic evolution of the region defining the role played by the main tectonic alignments on the present geomorphic setting

a sault outlet referenced mid to late holocene paleohydrograph for lake superior constructed from strandplains of beach ridges the most detailed lake superior paleohydrograph relative to the current outlet near sault ste marie ontario michigan was constructed from four strandplains of beach ridges this provides a history of water level glacial isostatic adjustment gia and the active outlet prior to monitoring and regulation four relative paleohydrographs that are offset and subparallel owing to differences in gia were produced from 321 basal foreshore elevations and 56 optically stimulated luminescence ages subtracting modeled elevations in defined millennial lake phases between relative paleohydrographs and similarity between an inferred sault ste marie hereinafter sault paleohydrograph and data near the zero isobase corroborates rates of gia derived from water level gauges a change in trend in the sault paleohydrograph is related to the final separation of lake superior from lakes michigan and huron and is the youngest age reported at 1060 100 years a near horizontal trend in the sault paleohydrograph for the past millennium has an intercept that is close to the historical average for lake superior a consistently linear trend from about 2 to 1 ka suggests a relatively stable outlet similar to the past millennium but a decreasing trend from 3 to 1 ka suggests an outlet other than the sault although intercept data beyond the last millennium are similar in elevation to the reported bedrock sill near chicago hansel et al 1985 we argue that the port huron outlet was the active outlet during this time and the inferred paleohydrograph of baedke and thompson 2000 requires reevaluation resume le paleo hydrogramme le plus detaille pour le lac superieur par rapport a l exutoire actuel pres de sault ste marie ontario michigan a ete construit apartir de quatre anciennes plaines intertidales de cretes de plage ces donnees fournissent un historique du niveau de l eau de l ajustement isostatique glaciaire et d un exutoire actif avant le suivi et la regularisation quatre paleo hydrogrammes relatifs decales et subparalleles en raison de differences d ajustement isostatique glaciaire ont ete produits a partir de 321 elevations de base de l estran et 56 ges determinees par luminescence optique stimulee la soustraction des elevations modelisees dans des phases de lac millenaires definies entre des paleo hydrogrammes relatifs et la similitude entre un paleo hydrogramme infere pour le sault ste marie sault ainsi que les donnees aproximite de l isobase zero corroborent les taux d ajustement isostatique glaciaire derives de jauges de niveau d eau un changement de tendance dans le paleo hydrogramme du sault est reliee a la separation finale du lac superieur du lac michigan huron et constitue le plus jeune ge rapporte soit 1060 100 ans une tendance presque horizontale dans le paleo hydrogramme du sault pour le dernier millenium a un intercepte qui est pres de la moyenne historique pour le lac superieur une tendance lineaire constante depuis 2 a 1 ka suggere un exutoire relativement stable semblable acelui du dernier millenaire mais une tendance decroissante depuis 3 a 1 ka suggere un exutoire autre que celui du sault bien que les donnees d intercepte au deladu dernier millenaire aient une elevation semblable a celle rapportee pour le seuil de socle rocheux a proximite de chicago hansel et al 1985 nous proposons que l exutoire port huron constituait l exutoire actif acette epoque et que le paleo hydrogramme infere de baedke et thompson 2002 demande a etre reevalue traduit par la redaction

a microtremor survey to define the subsoil structure in a mud volcanoes area the case study of salinelle mt etna italy a microtremor survey aiming to obtain information on subsoil structure was performed in the lower southwestern etnean flank sicily italy the area is characterized by emissions of muddy and salty water which create specific pseudo volcanic edifices recording sites were both randomly selected in the area and along two profiles horizontal to vertical noise spectral ratio polarization and surface wave prospecting techniques were used the spectral ratios results set into evidence different frequency ranges that appear interesting to infer information on the subsoil structure the depth of the hydrocarbon reservoir was inferred through 1d modeling by using the information coming from the literature and experimental surveys moreover a strongly directional effect suggests the existence of a nnw sse oriented mud feeding dike

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

kinematics and dynamics of the late quaternary rift flank deformation in the hyblean plateau se sicily abstract the southernmost branch of the siculo calabrian rift zone scrz in se sicily is flanked by an actively uplifting 31 km wide and 40 km long rectangular shaped crustal block siracusa domain sd whose late quaternary tectonic evolution has been controlled by the active nw verging thrusting along its northwestern margin accompanied by an extension on the opposite side within the mobile block a local extensional stress field has produced two n140 oriented late quaternary collapsed basins which opened roughly perpendicular to the direction of stretching along the scrz some tectonic peculiarities of the sd such as the occurrence of shortening in absence of a crustal back stop the coexistence of local extensional and contractional stress field and the primary role played by fluids in the deformational processes suggest a possible connection between the shallower crustal dynamics with a deep seated mantle intrusion beneath the region as it is commonly documented to occur along the rift zones where the rift flank volcanism develops similar dynamics and kinematics have been in fact described in the adjacent areas of the western flank of scrz which are affected by volcanism e g eolian islands and mt etna the results of our study in the hyblean region give thus the opportunity to detail on the mode and the mechanics of faulting that can be significant to interpret the seismicity and active deformation in the adjacent volcanic areas of sicily

eastern pacific ocean circulation near the onset of the 1982 1983 el nino over a 1 month period october 5 to november 6 1982 during the initial stages of the 1982 1983 el nino hydrographic and velocity profiling measurements were made in the eastern equatorial pacific by two research vessels track lines approximated a square centered near the galapagos islands with approximately meridional sections at 95 w and 85 w and nearly zonal sections at about 5 n and 5 s water mass characteristics and estimated currents of these sections are discussed sea surface temperature nearly everywhere was warmer than 25 c an anomaly of 2 c 3 c the equatorial thermocline represented by the 20 c isotherm was depressed by nearly 50 m at 85 w and more than 100 m at 95 w relative to a historical mean profile across 95 w estimated geostrophic relative to 500 dbar and directly measured near equatorial velocity profiles indicated significant eastward surface flow the south equatorial current south of the equator had disappeared estimated warm water transport t 24 5 kg m 3 indicated an influx into the region which was approximately that required to balance the observed low frequency sea level change at the galapagos islands temperature and salinity properties as well as the transport estimates indicated that this warm water came predominantly from the west

a refined gravity model from lageos gem l2 a refined gravity field model goddard earth model gem l2 has been derived using the lageos orbital data yielding better baseline measurements for the analysis of tectonic plate motion this field also contributes to an improved understanding of long wavelength features such as the sea slope across broad ocean basins through its significant improvement of the long wavelength geoid through degree and order 4 the geoid for these terms has an accuracy estimated at 8 cm in gem l2 gem l2 as in all recent goddard earth models relies heavily on the precise near earth satellite laser ranging data in this case provided by nasa s crustal dynamics program two and a half years of lageos laser data acquired from over 20 well distributed stations were combined with the existing data from the best satellite derived model gem 9 to develop the new lageos model testing shows that the lageos gravity field error at long wavelengths is less than half that for gem 9 independent tests using well determined longitude accelerations of 24 hour satellites have verified the improved accuracy of the new model a comparison of global laser base stations from independent data sets of alternating 15 day data segments over the 2 1 2 years of lageos show total inter station positioning to 1 8 cm when using this new field the same comparison using the 1979 versus the 1980 lageos data yields 5 2 cm this difference in agreement reflects the change in data distribution and other systematic errors along with the tectonic motion which has occurred between these chronologically distinguishable data sets five day average polar motion values with a precision of 10 cm and change in length of day values accurate to better than 5 msec have been derived in the solution the adjustment of these parameters are necessary to achieve the accurate stations and geopotential results in gem l2

precision geodesy and geodynamics using starlette laser ranging the starlette satellite launched by the french centre national d etudes spatiales in 1975 has provided an important means for deriving geodetic and geodynamic parameters from near earth satellite laser ranging data we report here on the development of a gravity field specialized for starlette designated pgs 1331 using the data from 1975 through 1978 we further report on the detailed analysis of the 1980 starlette laser ranging data for the estimation of tracking station coordinates polar motion gravitational constant gm and other parameters these analyses illustrate the improvement in our geodetic and geodynamic modeling provided by pgs 1331 data fits for 5 day orbital arcs have been improved from the level of several meters to a few decimeters comparisons of the station coordinate values derived from starlette with those from independent lageos solutions indicate an rms agreement of about 25 cm these analyses have provided an independent check of the lageos derived center of mass tracking station coordinates

sedimentary and tectonic evolution of the eastern hyblean plateau southeastern sicily during late cretaceous to quaternary time abstract two palaeogeographic domains have been distinguished in the cretaceous quaternary sequences which crop out in the hyblean region of southeastern sicily in the northeast shallow water algal bryozoan calcarenites of oligocene miocene age overlie either cretaceous rudist limestones or volcanics further to the northeast the stratigraphic gap increases as the miocene limestone thins and in the a g i p well catania 10 plio pleistocene sediments and volcanics directly overlie upper jurassic rocks in the southwestern part of the hyblean plateau pelagic sediments occupy the cretaceous miocene interval they were deposited in a shallow basin dipping gently towards the southwest the transition between the two zones is marked by much evidence of synsedimentary tectonic activity such as widespread slumping and the development of megabreccias composed of cretaceous and eocene blocks the palaeogeographic picture is one of carbonate reefs and volcanic seamounts developing in the upper cretaceous they formed platforms fault bounded to the west and southwest from which were derived the detrital sediments found in the basin and occasional spectacular gravity slides in present day terms the structural high probably corresponds to the northeastern margin of the hyblean plateau and in part to the siracusa syracuse malta escarpment the pattern is little changed in the upper miocene with volcanoclastics of phreatomagmatic origin intercalated with coral bioherms overlying algal bryozoan calcarenites upper tortonian lower messinian limestones with a restricted fauna indicate a shallow water environment which grades up into continental conditions in the eastern hyblean plateau the tertiary sequence is capped by pliocene submarine to subaerial mafic lava flows lower pleistocene sediments consist of biocalcarenites and clays which fill deep graben delimited by plio pleistocene faults the inshore continuation of the malta syracuse escarpment system of faults from a tectonic standpoint the hyblean region a gently deformed segment of the african continental margin acted as a foreland during tertiary times a cretaceous eocene tectonic phase was responsible for the palaeogeographic pattern which existed during most of the cenozoic the present pattern is the result of three main tectonic phases following the regional upper miocene uplift of early middle pliocene plio pleistocene and middle pleistocene recent age which influenced the tectonic evolution of the present ionian coast and the malta syracuse escarpment

the earth s gravity field and plate tectonics abstract a recent decomposition of the earth s gravity field has allowed mass anomaly sources spatially related to plate tectonic features to be distinguished from those mass anomaly sources that are not the earth s largest mass anomalies are not related the mass anomalies contributing to the degree 2 3 field are inferred to be the result of topography at the core mantle boundary produce the world s largest geoid anomalies and are unrelated to the plate tectonics occurring at our planet s surface the degree 4 10 field shows major narrow bands of positive geoid anomalies with marked coincidence everywhere with plate convergence zones the degree 4 10 mass anomaly appears to lie in the lower mantle beneath plate convergence zones below the teleseismically determined downgoing subducted slabs and may be an important driving force for plate tectonics contributing to the stabilization of the location of subduction zones through time subtracting the degree 10 field from observed data yields residual anomalies both the residual geoid and gravity anomalies result entirely from mass anomalies that lie in the outer part of the earth the residual geoid anomalies have much lower magnitude than those of the degree 2 3 and 4 10 fields axes of spreading in the indian ocean in the north atlantic and partially in the south atlantic lie along centers of positive residual geoid and gravity anomalies the east pacific rise is without expression presumably because of its fast spreading rate with broad topography fracture zones are commonly well defined because of their linearity although their geoid and gravity amplitudes are small amongst spreading centers without superimposed hot spots fracture zones and subduction zones the subduction zones have the largest residual gravity anomalies although their residual geoid anomalies are generally less than 20 m their residual gravity anomalies of 200 to 350 mgal show them to be the sites of the largest magnitude gravity anomalies of our planet residual geoid anomalies associated with the elevated topography of hot spot features reach 22 m

a simplified analysis of the total seismic hazard in italy abstract total seismic hazard assessment i e the base hazard modified by local site conditions plays a key role in seismic risk prevention and mitigation this is an important topic due to the impact of a reliable hazard assessment on the resilience of local communities in the case of an earthquake this paper presents a study that evaluates the total seismic hazard for the entire italy excluding the island of sardinia the results are expressed in terms of amplification factors and total hazard parameters to this end soil characterisation was performed firstly using italian seismic network data for 259 sites uniformly distributed across italy and secondly using the mean value of the shear wave velocity available from a global dataset produced by the united states geological survey the amplification effects were quantified according to i an approach consistent with the italian building code and ii one dimensional site response analyses these two procedures are referred to as parsimonious and rigorous here respectively the results indicate a generally satisfactory match between the estimates obtained by means of these two procedures for periods lower than 0 5 s while parsimonious procedures at periods longer than 0 5 s provide an upper limit on the total seismic hazard finally a seismic classification in terms of the classes of total hazard parameters is proposed for the italian peninsula area

empirical evidence of orthogonal relationship between directional site effects and fracture azimuths in an active fault zone the case of the mt etna lower eastern flank abstract mt etna in eastern sicily is a composite active volcano whose eastern flank is affected by several normal and strike slip active faults in this study geological structural field survey and ambient vibration measurements are performed in the lower eastern flank of mt etna in order to define the role of the tectono stratigraphic setting in the seismic site response the sites of measurements are mainly distributed inside the few hundreds of meters long s caterina graben which is located between two main seismogenic active faults of this volcano sector the acireale and the fiandaca faults our study aims at defining the contribution of the fault related active deformation in determining the local ground motion amplification also providing a subsoil geological model based on the integration of geological and geophysical investigation therefore structural measurements were made in seven sites revealing coseismic and aseismic extensional fractures mainly striking nnw the seismic site response was studied processing the ambient vibration measurements through horizontal to vertical spectral ratio the measured fundamental frequency falls in the range 1 0 4 0 hz that we linked to the presence of a velocity contrast at depth of 80 200 m by calibrating a frequency depth function moreover the seismic site effect is due to the stratigraphic setting and is markedly directional showing maximum amplification along the direction orthogonal to the strike of the observed isooriented extensional fracture field produced by the activity of the s caterina graben it is noteworthy that far from the graben on sites of measurements located near the fiandaca fault we observed directional effects parallel to the direction of maximum extension inferred for this tectonic lineament our results suggest a linkage between directional site effects and local stress tensors and fractures field orientation

the termination of the equatorial undercurrent in the eastern pacific abstract the termination of the equatorial undercurrent euc in the eastern tropical pacific has been studied through analysis of the historical hydrographic station data in the region bounded by 5 n 10 s 80 w and 100 w three distinctive hydrographic features associated with the euc are used along with dynamic topography to trace the mean path of the euc and to investigate aspects of its seasonal variation these features are 1 the 13 c thermostad 2 the high salinity core and 3 the high dissolved oxygen concentration tongue the thermostad is thickest just south of the equator to the west of the galapagos islands with a decreasing maximum extending southeast to the coast of south america near 7 s the thermostad is poorly developed in the mean near the equator east of the galapagos islands this pattern appears to be produced by convergence of eastward flow in the euc and in the southern subsurface countercurrent as the euc flows southeastward from the galapagos this interpretation is supported by the geostrophic flow calculated from the mean dynamic topography the isolated high salinity core is found to the south of the equator and is traced all the way to the coast of south america the high oxygen tongue associated with the euc splits at the galapagos with the southward projecting branch disappearing rapidly as an identifiable feature the other branch of the tongue continues around the islands to the north and along the equator to the coast of ecuador some evidence of recirculation of euc water in the south equatorial current is seen to the northwest of the galapagos a strong seasonal pulsation of the euc affects these features in a consistent way with the pulse occurring first west of the galapagos and later along the coast the thermostad first reaches maximum development and then a pronounced downwelling of the thermocline occurs rapidly leading to minimum thermostad extent associated wtih this downwelling is an eastward protruding high salinity tongue near the equator which is later seen as an isolated core along the coast at 4 s and 6 s pressure gradients along the equator and the coast inferred from dynamic topography suggest that this pulse is associated with an increase in the flow of the euc and ultimately the peru chile undercurrent the pressure gradient reversal along the equator occurs prior to the annual wind reversal suggesting that remote forcing plays a role in the seasonal pulse of the euc in the eastern pacific

vertical crustal motion determined by satellite altimetry and tide gauge data in fennoscandia 1 we present a new method of combining satellite altimetry and tide gauge data to obtain improved estimates of absolute or geocentric vertical crustal motion at tide gauges within a semi enclosed sea as an illustration we combine topex poseidon altimetry data 1992 2001 and 25 long term 40 years tide gauge records around the baltic sea region of fennoscandia an area where crustal deformation is dominated by glacial isostatic adjustment gia a comparison of the estimated vertical motion at 1 11 mm yr with independent solutions from 10 collocated bifrost gps sites shows a difference of 0 2 0 9 mm yr thus verifying the accuracy and robustness of the procedure the solution uncertainty is estimated at 0 4 mm yr which is significantly lower than previous analyses of this type we conclude that our technique can potentially provide accurate vertical motion observations globally where long term tide gauge records exist

using h v measurements to determine depth to bedrock and vs30 in boston massachusetts abstract seismic microzonation is an important step in seismic risk and loss studies for densely populated urban regions ambient noise studies using h v measurements to determine the fundamental site period fsp can be an inexpensive and efficient method to map site effects for a microzonation study ambient noise studies are particularly effective in high impedance contrast environments like boston massachusetts where the soil depth ranges from 1 to 80 m and the soil shear wave velocity vs 200 m s overlays hard glacial till or bedrock vs 2000 3000 m s in this study ambient noise data were collected from 570 locations in the greater boston area nakamura s technique taking the ratio of the fast fourier transform fft of horizontal components to vertical components is applied to determine the fsp the fsp data are mapped across the region and show a consistent pattern with the local geologic and geomorphologic conditions the fsp data are then paired with depth to bedrock and vs30 drawn from 2403 boring logs and 25 vs profiles vs30 is defined as the time weighted average of the vs in the upper 30 m of the soil profile the depth to bedrock and fsp are correlated as are fsp and vs30 measurements fsp depth to bedrock and fsp vs30 correlations are reported with 95 confidence bounds for use in regional planning the resulting fsp vs30 correlation is comparable with similar studies from high impedance contrast regions in canada and japan and show lower vs30 for sites with fsp 0 2 s where the fsp predicts depth to bedrock 18 m than previously reported for the nga west2 database the accuracy of single station ambient noise results is also confirmed with single station and vertical array earthquake spectral ratios an fsp 0 74 s was calculated from ambient noise data at the northeastern university neu vertical array site in the back bay of boston at this site the sediment thickness is 51 m and is consistent with the fsp 0 73 s calculated for the site using earthquake records from the 2011 mw 5 8 mineral virginia earthquake overall the outcomes of this study demonstrate that ambient noise studies can be used in high impedance contrast environments to reliably and consistently estimate the fsp when the fsp estimates are paired with additional data such as depth to bedrock vs30 estimates and recorded ground motion data the spatial distribution of regional site effects can be characterized

isopycnal eofs in the azores current region a statistical tool fordynamical analysis and data assimilation abstract an empirical orthogonal function analysis of the vertical space time variability of the thermohaline structure of the ocean in summer and fall 1993 in the azores current region has been performed the analysis used data from ctd casts of the semaphore intensive experiment referred to as a seasonally varying climatology the relative merits of depth coordinate and isopycnal coordinate representations have been examined in regard to the quality of identification of physical processes and to the effectiveness of the extrapolation from a sea level anomaly in an attempt to improve the treatment of the vertical dimension in oceanic assimilation problems the isopycnal eofs consistently proved more efficient in capturing the vertical structure of both dominant processes in the area of investigation the variability linked to the mediterranean water and the coherent physical system made up of the azores front and the azores current the isopycnal analysis also proved more robust when meddies mediterra

mass heterogeneities and convection in the earth s mantle inferred from gravity and core mantle boundary irregularities mass heterogeneities in the earth s mantle are retrieved from the gravity data and the topography of the core mantle boundary as well as the topography of the earth s surface a mantle circulation induced by the heterogeneities is modelled by solving the stokes problem for incompressible newtonian fluid the derived models of mantle motions correlate well with the plate tectonics and point at a close relation between the surface tectonic activity and the processes in the vicinity of the core mantle boundary

variability of lake michigan water level during the past 1000 years reconstructed through optical dating of a coastal strandplain post nipissing phase strandplains of the great lakes reflect late holocene water levels that are linked to climate variability glacial isostasy and changes in basin hydrology this study examines a strandplain sequence at bailey s harbor door county wisconsin along lake michigan which contains a record of water level variations during the past 1000 years following the separation of the lake michigan huron basin from the lake superior basin vibracores are used to define the current elevation of the foreshore facies in 25 preserved beach ridges optical ages for five individual beach ridges are compared with radiocarbon ages on basal peats from nine swales collected in a previous study the optical chronology yields a ridge formation preservation rate of 30 2 yr ridge similar to that of previous assessments this study further demonstrates the efficacy of optical dating for deciphering late holocene beach ridge sequences providing multidecadal resolution lake level meets or exceeds by at least 0 5 m historic metrics at c ad 1125 1225 the maximum water level after c ad 1225 is comparable with that recorded by the instrumental data there is a noticeable high lake level from c ad 1560 to 1725 dating of additional sites along lake michigan is required to establish local rates of glacio isostatic adjustment identify possible erosion of the outlets and to resolve lake level records for individual lakes following the separation of the upper great lakes currently constrained to have occurred c 2400 to 1200 years ago

radial variations of a satellite orbit due to gravitational errors implications for satellite altimetry the linear perturbations of the radius of a satellite orbit due to the geopotential are derived from these estimates are made of the radial orbit error due just to geopotential errors from current models employing only conventional satellite tracking data the estimates show that about an order of magnitude improvement in the satellite geopotential will be necessary to utilize the full accuracy of independent satellite altimeter measurements the linear perturbations are used to show that 1 a substantial improvement in the low degree geopotential is possible from the indirect use of seasat altimetry at track crossovers and 2 a separation of permanent sea topography and geoid may be possible from direct use of the heights along the track

dynamic role of a westerly wind burst in triggering an equatorial pacific warm event abstract dynamical impacts of a strong westerly wind burst wwb are studied using an ocean atmosphere coupled simulation in which an intense westerly wind burst is introduced the ocean response includes local and remote components with the development of a zonal surface jet and the appearance of positive sea surface temperature anomalies in the eastern pacific as observed during the triggering of the 1997 98 el nino remote warming results from the eastward propagation of a subsurface temperature anomaly generated in the western pacific a detailed heat budget helps to describe and understand the major mechanisms taking part to the formation of the subsurface temperature anomaly in the western pacific contributing to its eastward propagation and leading to the surface warming simulated in the eastern pacific advective contributions are proved to be widely predominant in the heat budget further decomposition of advective terms into linear and nonlinear parts allows insights into the role of mean stat

earth orientation from lunar laser ranging and an error analysis of polar motion services the rotational orientation of the earth has been determined from lunar laser ranging llr measurements acquired at mcdonald observatory in texas the values and uncertainties of ut0 are calculated from 1971 through may 1982 in four forms raw results on 799 separate days kalman filtered values gaussian smoothed values and fourier smoothed values the effects of the different smoothings are assessed llr being dominated by a single station operation is sensitive to one projection of polar motion the component along the mcdonald meridian variation of latitude results are presented for the polar motion component along the mcdonald meridian analyses of the llr data assess the errors of polar motion sources bureau internationale de l heure bih defense mapping agency hydrographic topographic center dmahtc doppler the international polar motion service ipms lageos goddard space flight center gsfc lageos university of texas texas and the lerch analysis of artificial satellite data the rms errors of both the llr data and the determination of polar motion by the various services decrease in recent times for data taken from august 1976 through may 1982 doppler and bih values are of comparable quality estimated error doppler 20 5 cm bih 22 4 cm with ipms results being somewhat larger 38 5 cm lageos polar motion error drops in early 1979 in both analyses gsfc 14 7 cm texas 18 6 cm for data from february 1979 through may 1981 this drop parallels instrumental improvements and the increased number of stations in the laser system the doppler polar motion error 17 5 cm is especially low for the period may 1977 through february 1981 the analysis of lerch february 1979 through may 1981 gives an error estimate of 14 7 cm all analyses are consistent with 11 cm as an estimate for the combined llr modeling fitting and instrumental error noise for august 1976 to may 1982

hydrographic variability west of the galapagos islands during the 1982 1983 el nino abstract nine hydrographic temperature salinity and in some cases oxygen and four zonal velocity sections near the equator along 95 w in 1980 1984 are presented and discussed perturbations associated with the 1982 1983 el nino form the locus for the discussion this event was sampled by sections in november 1982 and in march may november and december 1983 the upper ocean response in november 1982 was a downward displacement of isotherms above 400m on the equator the equatorial undercurrent euc was deep and strong for this season the vertical displacement perturbations extended to at least 5 s and were more uniform with depth off the equator in may 1983 the largest vertical displacements were observed the euc was replaced by a westward jet at about 75m and the equatorial 13 c water thermostad has disappeared local estimates of the zonal pressure gradient suggest that between 110 w and 95 w this slope had reversed in may 1983 and was at least in part responsible for the observed westward jet local winds were westerly and forced the observed eastward surface current by november 1983 surface conditions were fairly normal however the deeper stratification remained anomalous the equatorial 13 c water thermostad was still missing the vertical profile of vertical displacements from a mean suggested a complicated vertical structure near the equator in april 1984 conditions had returned to near normal

a comparison between lageos laser ranging and very long baseline interferometry determined baseline lengths the nasa crustal dynamics project uses satellite laser ranging slr and very long baseline interferometry vlbi data collected and analyzed by the goddard space flight center and the jet propulsion laboratory for the measurement of geodynamic and geodetic parameters an important parameter is the determination of the baseline length or intersite distance since october 1979 baselines determined from slr data and vlbi data have been compared to help assess the accuracy of the baseline measurements from these independent techniques eight locations in the continental united states participated in the comparison westford massachusetts fort davis texas platteville colorado and quincy owens valley goldstone pasadena and monument peak california twenty two baseline lengths between these locations as determined by slr were differenced from the corresponding vlbi determinations the rms scatter about zero for the length differences is 5 2 cm with a mean of 1 0 1 1 cm and there is no apparent scale factor between these two distance determinations for this result the monument peak quincy baseline has been adjusted for tectonic plate motion by using the slr determined baseline rate for the eight other baselines crossing a plate boundary tectonic motion was not modeled if a model for this motion based upon baseline changes derived from strain rates is applied the rms scatter about zero for the 22 differences becomes 7 2 cm with a mean of 1 0 1 1 cm the above results are within the combined error budgets of the slr and vlbi baseline length determinations

recent progress in the application of satellite altimetry to observing the mesoscale variability and general circulation of the oceans recent progress in the application of satellite altimetry from seasat and geos 3 to the observation of the oceanic mesoscale variability and general circulation is reviewed the lack of accurate geoid models has been the major obstacle in the study of the general ocean circulation from altimetry the use of geoid independent methods that utilize the temporal differences in altimetric measurements taken at fixed locations however has made significant contributions to our knowledge of the mesoscale variability of the ocean the mesoscale energies of the sea surface height and geostrophic current have been mapped on a global basis their distributions in wave number space have also been analyzed because of many of the deficiencies of existing altimeter data short duration inadequate orbit poor accuracy etc most of these results describe only a small portion of the frequency wave number spectrum of the variability but they have nonetheless demonstrated the great value of an optimally designed altimetric mission in advancing our knowledge of the global mesoscale variability the current technology allows satellite altimetry to detect oceanic variability at periods from a few days to 3 5 years and wavelengths from 50 to 10 000 km determining the time averaged general ocean circulation from altimetry is more problematic because an accurate geoid is indispensable the currently available global geoid models have useful accuracies only at wavelengths greater than about 7000 km there have been several attempts at mapping the global ocean circulation at those scales using existing altimeter data and geoids when these results are compared with hydrographic surveys some qualitative agreement can be observed but the quantitative differences are mostly inconclusive because of the geoid and orbit errors it has been suggested however that an altimetric mission that is optimally designed with the current technology when complemented by a state of the art gravimetric mission to map the earth s gravity field is able to determine the ocean circulation quantitatively at scales from the ocean basin to about 200 km

comprehensive ambient noise analyses for seismic microzonation of sarpol e zahab after the mw 7 3 2017 iran earthquake abstract this study is intended to investigate ambient noise recordings in form of array and single station measurements at sarpol e zahab city after the destructive mw 7 3 earthquake of 12 november 2017 in kermanshah province iran the espac f k hvtfa and hvsr methods are applied to analyze the ambient noise and obtain useful information on three key factors of site seismic properties i e the geometry of ground layers their mechanical characteristics and site resonance frequencies the results of this study are presented as maps of the fundamental frequency of the ground depth of bedrock the thickness of top cover materials as well as the average shear wave velocity vs 700 and vs 30 for sarpol e zahab the analyses show that the single value of vs 30 does not represent seismic ground response and the depth of competent bedrock which dominates the low frequency seismic response amplifications is located far beyond 30 m in this city the most effective grade ii seismic microzonation of sarpol e zahab is provided by combining the results of these analyses

rise of great lakes surface water sinking of the upper midwest of the united states and viscous collapse of the forebulge of the former laurentide ice sheet

an overview of local site effects and the associated building damage in adapazari during the 17 august 1999 izmit earthquake two major earthquakes occurred in turkey along the north anatolian fault in 1999 the first one which occurred on 17 august 1999 had a moment magnitude of 7 4 and ruptured the 140 km segment of the fault in the marmara region adapazari a city with a population of 190 000 which is mostly located on a deep alluvial basin in the near field of the ruptured fault was among the worst affected urban areas in the earthquake affected region the distribution of damage over the city was highly nonuniform indicating the variability of the ground response to the strong motion five to six story buildings located over deep alluvial soils were most adversely affected by the earthquake geotechnical characteristics of the alluvial basin of adapazari are evaluated using the deep and shallow borehole logs and the measured parameters from the field and laboratory this data is used for developing representative one dimensional site response models for various depths of alluvium and for liquefaction assessment in saturated surface soils recorded data from several aftershocks are utilized for model calibration the results of soil response studies are found to be highly correlated with the general trends in the intensity and distribution of building damage based on in situ tests soil liquefaction is determined to have occurred extensively in adapazari which is in conformity with the postearthquake observations of widespread liquefaction induced foundation displacements evidently liquefied soil layers served as passive isolation mechanism for numerous buildings some of which were subjected to excessive foundation displacements of various forms without signs of significant structural damage manuscript received 30 august 2000

the vertical structure of the zonal pressure gradient in the eastern equatorial pacific ctd data from the epocs and norpax experiments were used to construct a mean zonal pressure gradient profile between 110 w and 150 w for the 1979 to 1981 pre el nino time period the mean zonal pressure gradient referenced to 100 dbar had a value of 4 5 10 7 m s 2 at the surface and decreased to within two standard errors of zero at 200 dbar below this depth the mean was not significantly different from zero deviations from this mean were not related to fluctuations of the zonally averaged zonal wind stress between 150 w and 110 w rather the largest deviations in the boreal springs of 1979 and 1980 appeared to be associated first with vertical mode kelvin wave pulses propagating eastward along the equator the 1979 81 mean profile was also used as a reference to examine variations in zonal pressure gradient during the 1982 83 enso event the sea surface was more sharply sloped upward from the east to west in april and september 1982 before arid near the beginning of the event the surface slope was below normal in april and october 1983 vertical profiles of the zonal pressure gradient deviations showed large high vertical mode contributions during the vent than in the prevent samples

vlbi baseline variations from the ice 4g model of postglacial rebound an analysis is presented of selected vlbi baseline variations expected as a consequence of the continuing process of glacial isostatic adjustment although these baseline variations are for the most part dominated by the radial component of the motion the tangential component can also be an important contributor to the net effect and is in fact dominant for short baselines the new calculations have been performed with the recently derived ice 4g model of the last deglaciation event of the current ice age peltier 1994 and the results demonstrate that those obtained with the previous ice 3g model are not reliable

correlation of current and sea level in the eastern equatorial pacific abstract upper ocean current and temperature records from neat 0 110 w are compared with galapagos island sea level measurements 0 3 s 91 28 w for the period march 1980 to july 1981 low frequency periods greater than 30 days near surface zonal currents 20 and 50 m were well correlated with local wind but deeper currents 100 and 150 m and sea level were not response to the local wind was studied in terms of linear dynamics periods where zonal acceleration was in phase with zonal wind stress were found however overall these two series were uncorrelated the direct relation of low frequency wind stress and surface current rather than acceleration suggests a quasi equilibrium response on these time scales the response at deeper levels was investigated by comparing the zonal transport per unit width vertically averaged zonal velocity in the upper 200 m with sea level these series were significantly correlated with 95 confidence at a lag of 10 5 d indicating eastward phase propagation

the origin of large scale structure in mantle convection effects of plate motions and viscosity stratification convection in earth close quote s mantle is dominated by long wavelength structure as evidenced by the very open quote open quote red close quote close quote spectra of both seismic velocity heterogeneity in the deep mantle and the non hydrostatic gravity field or geoid here we show that this large scale structure may be a consequence of two factors that influence the scale of mantle convection first the existence of surface plates which tend to organize the flow second a substantial increase in lower mantle viscosity for which there is considerable independent geophysical evidence combining these two factors in 3 d spherical mantle convection models explains rather well the observed seismic spectrum of mantle heterogeneity copyright american geophysical union 1996

global positioning system testing of geoids computed from geopotential models and local gravity data a case study oithometric height differences obtained from a combination of global positioning system gps ellipsoidal height differences and gravimetric geoid predictions have the potential of replacing costly and time consuming spirit leveling especially in remote unsurveyed areas like the canadian north in this paper 88 gps stations along a 900 km long first order leveling line around the great slave lake area northwest territories canada are used as control for intercomparison of geoid predictions which used various geopotential models and gravimetric techniques the global spherical harmonic models tested include satellite only solutions such as gem 9 gem l2 gem tl and gem t2 as well as combination solutions such as gemlob rapp78 rapp81 gpm2 osu86f osu89a osu89b and osu91 a these models fit the geoid with standard errors of 30 to 50 cm local gravimetric geoid predictions based on available gravity data were carried out using various forms of stokes integration fast fourier transform methods and least squares collocation for the first two methods gravity data were gridded on a 5 km by 5 km cartesian grid and on a 5 by 10 geographical grid no terrain reductions were applied due to the flatness of the topography results show that the differences between control and predicted geoid heights have standard deviations at the 20 to 25 cm level with differences between methods at 2 to 8 cm 1 by fitting a four parameter model to the geoid predictions corresponding to a gps leveling or geoid datum shift and scale change long wavelength errors were significantly reduced with all methods yielding geoid fits of about 7 cm 1 the relative accuracies achieved were of the order of 2 ppm for baselines shorter than 200 km and of the order of 1 ppm for baselines with lengths between 200 km and 700 km a discussion of possible error sources concludes the paper some errors in the original gps data were detected in the initial phase of the project and a gps resurvey verifyed these errors

the calculation of the dynamic sea surface topography and the associated flow field from altimetry data a characteristic function method the quasi stationary sea surface topography qsst and associated oceanic circulation is determined by means of a characteristic function technique the method was originally implemented in an ideal simplified case the present application involves a 4 83 4 8grid in spherical coordinates approximating the boundaries of the main ocean basins the data field is provided by the first year of altimetric data from the topex poseidon mission the method requires the numerical determination of the eigenfunctions spanning the streamfunction field and the associated characteristic functions from the balance equation the former yields the flow field and the latter the surface height distribution or qsst these functions are determined by the geometry and topography of the ocean basins and satisfy the linear steady state dynamical equations they are defined within the basins only and avoid the problems encountered when using functions defined over the entire sphere the velocity field can be computed over the entire ocean area including the equatorial regions the coefficients of the height functions have been determined by fitting the surface height field provided by topex altimetry seasonal variations have been computed by subtracting a 32 cycle solution from each of the four 8 cycle seasonal solutions

site specific issues for strong ground motions during the kocaeli turkey earthquake of 17 august 1999 as inferred from array observations of microtremors and aftershocks array observations of microtremors and aftershocks were carried out near the permanent strong motion observation sites and the damaged areas after the kocaeli turkey earthquake of 17 august 1999 the major objectives were to determine s wave velocity structures at the sites and to understand the site effects on strong motion or damage array observation of microtremors is a useful method for determining the s wave velocity structures in a sedimentary basin with less practical restriction than the other geotechnical methods the spatial autocorrelation method spac was applied to array data of microtremors for determining s wave velocity structures the spac method generally provides an equivalent result with that of the frequency wavenumber method using fewer array sites and a smaller array size most strong motion sites near the fault are classified into stiff and or very hard soils the records cannot directly be used for interpreting damage to buildings in the sedimentary basin records of long durations of strong motion at ats near avcilar west of istanbul are closely related to the low velocity v s 200 m sec of the surface layers the s wave velocity structure at avcilar where there was severe damage during the mainshock is similar to that of the lowland ats and it differs significantly from that of cna located 4 km northeast of avcilar where the strong motion record was obtained from the mainshock the strong ground motion at avcilar during the mainshock is estimated to be similar to that at ats of the strong motion sites sakarya skr is located on very hard soil whereas thick and soft sediments cover downtown adapazari it is plausible that strong ground motions during the mainshock in the damaged area adc were significantly different from those of skr a large difference between the strong motions of a hillside and the lzmit bay area in and around golcuk is also indicated by a comparison of aftershock records

numerical modeling of seismic site effects in a shallow estuarine bay suai bay shantou china abstract this paper presents the results of numerical modeling of seismic site effects in a shallow estuarine bay suai bay shantou china which is meaning for seismic hazard assessment and mitigation of estuarine and coastal structures such as immersed tunnels pipelines caissons and breakwaters the subsurface stratum and soil properties in the study area are obtained from geological and geotechnical surveys large scale 2d finite element refined nonlinear modeling is used to simulate ground motion for near field and far filed input motions with different design earthquake levels the results show that for the study area 1 the spatial distribution of pga amplification factor presents obvious vertical and horizontal variations and is strongly affected by the overall geometry of interfaces of different materials 2 the attenuation in soft sediments have significant influences on surface ground motion which leads to a deamplification of the acceleration amplitude a prolongation of the significant duration and a filtration of the high frequency spectral content 3 the pga alone cannot be regarded as an adequate parameter to quantify nonlinear site effects while the energy content expressed by arias intensity is more closely related to transfer functions patterns 4 the seismic intensity at surface is greater than the intensity of input motion during weak motions while the seismic intensity at surface is smaller than the intensity of input motion during strong motions suggesting that isolation effects may be expected in the areas having thick soft soils with a low plasticity index during strong motions

dynamic sea surface topography gravity and improved orbit accuracies from the direct evaluation of seasat altimeter data a gravitational model incorporating seasat altimetry surface gravimetry and satellite tracking data has been determined in terms of global spherical harmonics complete to degree and order 50 this model pgs 3337 uses altimeter data as a dynamic observation of the satellite s height above the sea surface a solution for the ocean s dynamic topography is recovered simultaneously with the orbit parameters gravity and ocean tidal terms the recovered dynamic topography reveals the global long wavelength circulation of the oceans with a resolution of 2 000 km and is very similar to the mean upper ocean dynamic height derived from historical ship observations the pgs 3337 geoid has an uncertainty of 60 cm rms globally but only 25 cm rms over the ocean because of the altimeter measurements seasat orbits determined in this solution have an estimated accuracy for the radial position of 20 cm rms the difference between the altimeter observed sea height and the geoid plus dynamic topography model is 30 cm rms contained in these residuals are the sea height variability as well as errors from the geoid orbits tidal models and altimeter range measurements this performance level is 2 to 3 times better than that achieved with previous goddard gravitational models

instrumental evidence of normal mode rock slope vibration summary a unique field experiment was performed to constrain the seismic response of a large potentially unstable rock slope in the southern swiss alps small aperture seismic arrays were deployed to record ambient vibrations both inside and outside of the mapped instability boundary the recordings were analysed by means of the high resolution f k method site to reference spectral ratios and time frequency dependent polarization analysis all three methods indicated that the wavefield within the potentially unstable rock mass is dominated by normal mode motion standing waves rather than horizontal propagation of seismic waves both fundamental frequency and relative amplification could be recovered from ambient noise data the observed amplification is strongly directional and the maximum amplification is oriented perpendicular to open tension cracks mapped at the ground surface our results highlight site response characteristics relevant for analysis of earthquake triggered rock slope failures

isopycnal empirical orthogonal functions eofs in the north and tropical atlantic and their use in estimation problems we investigated the vertical variability of the thermal dynamical structure of the north and tropical atlantic ocean from a set of historical hydrographic data reynaud et al 1998 the analysis was performed in 10 geographic bins in terms of vertical empirical orthogonal functions eofs in isopycnal coordinates as first proposed by gavart and de mey 1997 hereinafter referred to as gdm97 in the isopycnal coordinate system the state vector is made up of isopycnal displacements and the compensated potential temperature along isopycnals gdm97 showed that in the azores madeira region the isopycnal eofs consistently help to better separate physical processes in the water column and to better project the dynamic height anomaly downward in comparison with the classical eof analysis in depth coordinates in the present study we extended their work geographically and the connection with state estimation and data assimilation was more formalized from our results smooth spatial variations of isopycnal eofs were found in the north atlantic and confirmed the large scale relevance of isopycnal eofs in the ocean north of 20 n the dominant isopycnal eof was associated with a quasihomogeneous vertical displacement of the isopycnal surfaces 1 with a quasiconservation of compensated potential temperature on those surfaces 0 that mode was strongly modified by thermocline intensified baroclinic effects along the path of the gulf stream up to 40 w some physical interpretations of the vertical eofs were also suggested in several areas as far as the isopycnal formulation was concerned e g some thermal fronts the mediterranean outflow water lenses or meddies this work confirmed the validity of the ideas of gdm97 over the entire north atlantic ocean the potential use of the isopycnal eofs in state estimation problems was discussed they are possible candidates to reduce the order of state estimation problems provided that they have good observability properties these observability properties were studied in the case of satellite altimetry that is we examined how the dominant isopycnal eofs were connected to sea level anomalies in most bins it was found that the order of an estimation problem could be truncated to one primarily north of 20 n or two modes the dominant eof was found to account for most of the surface dynamic height variability with a rather normally distributed error of only a few centimeters dynamically more robust results were also presented performing a univariate isopycnal analysis in leaving coherent thermal effects out as a result the dominant character of mode 1 was further enhanced everywhere these univariate isopycnal eofs can be used for purely dynamical state estimation more generally we believe that our results can be used to set up reduced order data assimilation schemes in the north atlantic or in other regions with good historical data

correlation between earthquake damage and seismic site effects the study case of lentini and carlentini italy abstract on december 13th 1990 a magnitude 5 6 seismic event felt throughout sicily and having maximum seismic intensity vii viii occurred although it is classified as moderate magnitude it caused causalities and the collapse of a few buildings two of the most struck cities were carlentini and lentini located in south eastern sicily at about 20 km from the instrumental epicenter in order to evaluate the influence of ground features on the damage distribution both vulnerability and damage maps were drawn using information collected in about 6000 forms coming from official ascertainments significant damage observed in some portions of the investigated areas appears related to the modest quality of the buildings that were classified as medium to high vulnerability to evaluate the role played by the geologic setting two sites were instrumented to measure shear wave velocity of the main lithotypes sixty three ambient vibrations measurements were also performed both in free field and inside some buildings moreover using information coming from geological and geophysical surveys 1d numerical modelling were done to achieve information about the main ground motion parameters the results highlight the occurrence of significant site effects and the potential presence of resonance phenomena between site and structure during the occurrence of a seismic event seismic site amplifications together with the buildings vulnerability observed through damage surveys contributed to enhance the inherent seismic risk of the investigated area

analysis of gps measurements in eastern canada using principal component analysis continuous global positioning system cgps position time series from eastern north america constrain the pattern and magnitude of regional crustal deformation initial analysis delineates consistent uplift patterns as expected from glacial isostatic adjustment gia predictions but the associated horizontal deformation is not definitive in part due to the short time periods for a significant number of the available stations we employ an eigenpattern decomposition in order to define a unique finite set of deformation patterns for this continuous gps data similar in nature to the empirical orthogonal functions historically employed in the analysis of atmospheric and oceanographic phenomena the method derives the eigenvalues and eigenstates from the diagonalization of the correlation matrix using a karhunen loeve expansion kle the kle technique is used to identify the important modes in both time and space for the cgps data modes that potentially include signals such as horizontal and vertical gia tectonic strain and seasonal effects here we filter both the vertical and horizontal velocity patterns on different spatiotemporal scales in order to study the potential geophysical sources after the removal of correlated and random noise the method is successful in disaggregating the linear vertical signal from more variable and less spatially correlated signals the vertical and horizontal results are compared to the predictions of the ice 3g gia loading model with a number of plausible mantle viscosity profiles the horizontal velocity analysis allows for qualitative differentiation between several potential gia models and suggests that with longer time series this technique can be employed to remove correlated noise and improve estimates of crustal strain patterns and their sources

station coordinates baselines and earth rotation from lageos laser ranging 1976 1984 satellite laser range slr measurements to lageos from may 1976 to january 1984 have been used to compute earth rotation parameters and the geocentric positions of 57 laser tracking station sites occupied during this interval the station position determinations were part of a simultaneous solution which includes lageos orbit elements in 15 day arcs and earth rotation parameters in 3 day subarcs using residuals from a 7 7 year lageos long arc lla 8402 systematic differences between the terrestrial reference frames implied by the university of texas station coordinate solution lsc 8402 and by previous solutions computed at the university of texas ut and at goddard space flight center gsfc are reviewed the new solution resolves a 0 72 m z axis difference between the terrestrial reference system origins inferred from the gsfc solution sl5 and the previous ut solution lsc 8112 the implied origins of the lsc 8402 solution and the sl5 solution are consistent to less than 60 mm in all components and after removing orientation and scale differences the coordinates for 26 common tracking stations have an rms difference of less than 80 mm the rms difference in baseline length for 22 station pairs used in the recent crustal dynamics project very long baseline interferometry vlbi slr intercomparison experiment is 50 mm between the gsfc and ut laser solutions and 40 mm between the ut laser solution and the vlbi solution the earth rotation parameters computed in 3 day intervals have an internal precision of 2 marc sec 62 mm at the earth s surface for xp and yp and 0 15 ms 70 mm at the equator for ut1 the estimated accuracy of the series based on dual baseline vlbi intercomparisons is approximately 2 marc sec for xp and yp and 0 2 ms for ut1 the effects of plate motion on the determination of the secular drift in polar motion using the 7 7 year series is shown to be at the level of 1 marc sec yr finally baseline changes have been investigated by repeated station coordinate determinations using 60 day subsets of the 7 7 year interval of the lageos data set in each 60 day solution interval orbit elements were estimated at 15 day intervals and earth rotation parameters were determined at 5 day intervals for the 4 year period beginning in january 1980 baseline length changes inferred by the successive 60 day solutions were found to be in general agreement with the motions predicted by the am1 2 plate motion model of minster and jordan

effect of orbit error on determining sea surface variability using satellite altimetry satellite altimetry data provided by geos 3 seasat and currently geosat have been successfully used to measure sea surface variability the determination of the ocean variability has been accomplished through either examination of differences along collinear tracks or differences at points where tracks cross in either case it is first necessary to remove the relatively large long wavelength error that exists in the sea surface heights due to inaccuracies in the estimation of the satellite altitude from ground based tracking data this long wavelength altitude error has generally been an order of magnitude larger than the short wavelength variability that is being sought a number of techniques have been applied to eliminate the altitude error with the most common being a simple modeling of the orbit error as a linear trend over the region of interest the intent of this study is to quantify the effectiveness of using a linear model of altitude error when attempting to estimate sea surface variability although there are many sources of altitude error only the influence of gravity modeling errors will be considered here this is justified since this is the dominant error source in the estimation of the satellite altitude from ground based data additionally gravity model errors are the primary source of altitude errors with wavelengths shorter than once per revolution analyses are presented for the case of geosat and topex altitude errors due to the expected modeling uncertainties of the gem l2 and gem t1 gravity fields results are given in terms of the rms of the crossovers after removing linear trends along track and minimizing the crossovers it is found that for scales below 10 000 km both gravity models are equally effective also the higher altitude of topex provides for significantly better performance of the linear orbit error correction model the results indicate that the current gem t1 model induces crossover discrepancies of less than 5 cm rms at scales up to 10 000 km

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

a dynamic model of venus s gravity field unlike earth long wavelength gravity anomalies and topography correlate well on venus venus s admittance curve from spherical harmonic degree 2 to 18 is inconsistent with either airy or pratt isostasy but is consistent with dynamic support from mantle convection a model using whole mantle flow and a high viscosity near surface layer overlying a constant viscosity mantle reproduces this admittance curve on earth the effective viscosity deduced from geoid modeling increases by a factor of 300 from the asthenosphere to the lower mantle these viscosity estimates may be biased by the neglect of lateral variations in mantle viscosity associated with hot plumes and cold subducted slabs the different effective viscosity profiles for earth and venus may reflect their convective styles with tectonism and mantle heat transport dominated by hot plumes on venus and by subducted slabs on earth convection at degree 2 appears much stronger on earth than on venus a degree 2 convective structure may be unstable on venus but may have been stabilized on earth by the insulating effects of the pangean supercontinental assemblage

mass anomaly structure of the earth gravitational interaction is the weakest among the four known forces in the universe the particular gravity equipotential field that coincides with sea level is called the geoid and satellite data have revealed anomalies in its pattern that are puzzling to explain dynamic topography solutions have offered the preferred explanation for the past 15 years but problems remain an alternative explanation presented here contends that very large mass anomalies lie deep in the earth presumably produced by topography at the coremantle boundary cmb and only much smaller mass anomalies occur at shallower depths the principal distinction is whether one is willing to accept the possibility that processes within the earth s core may generate the cmb topography an analysis of the south american regional geoid high spherical harmonic degrees 2 10 indicates that only mass anomalies shallower than 1200 km are its cause this single positive source is contrary to dynamic topography solutions that would generate negative deflections of both the surface and the cmb in response to the positive subducted mass for the earth s fourth greatest geoid high our alternate explanation is tested utilizing a set of 9274 subduction 5 cube slab bloblet center points developed from reconstructed plate history that provide estimates of the locations of material subducted into the earth s mantle two global mass solutions are offered utilizing 1 only those bloblets in the outer 800 km and 2 only those bloblets in the outer 1400 km four point masses at 3000 km depth to simulate cmb topography produced by processes within the core unrelated to mantle dynamic topography complete the two mass models both models show reasonable agreement with patterns and magnitudes of the regional geoid and its component degree parts the model cmb mass anomalies are only a factor of 3 greater than those initially estimated by gravity to geoid ratios from observed values at geoid anomaly center locations difficulties with the dynamic topography solutions matters of the density of the subducted material the proper hydrostatic flattening value to use for analyses and possible causes for the cmb topography are discussed the subduction mass models are also used to estimate the magnitude of the driving force for plate tectonics 2 78 1020 to 3 23 1021 n approximately equivalent to 7 0 1012 to 8 1 1013 n m 1 these force values are comparable to published slab force estimates based on thermal considerations

a comparison of satellite doppler and gravimetric geoid undulations considering terrain corrected gravity data geoid undulations from satellite doppler stations have been compared to geoid undulations computed using three procedures the first procedure combines potential coefficients with uncorrected 1 1 free air anomalies in a 10 cap surrounding the computation point the second procedure uses the helmert second condensation procedure for anomaly reduction where terrain corrections and topographic indirect effects are considered the third procedure uses a set of potential coefficients to degree 180 after correcting the original doppler undulation for a 0 4 ppm scale change and a 4 m z axis bias comparisons were made at 10 sites located in mountainous areas of the western united states and 10 sites in the eastern united states where the topography was relatively flat the mean difference doppler minus gravimetric for the 10 western stations was 1 65 when no corrections were applied to the gravity data while the difference was reduced to 0 10 m when the terrain corrections and indirect effects were included for the 10 eastern stations the systematic difference excluding the negligible terrain effects was 0 42 m for western sites the standard deviation of the differences was 0 96 m with no gravity corrections and 0 93 m with the correction applied in the eastern sites the standard deviation was 0 55 m similar results were found with the potential coefficients to degree 180 our major conclusion is that the neglect of terrain corrections and to a lesser extent the indirect effect can cause systematic errors of the order of 1 5 m for a cap size of 10 in geoid undulations for stations in mountainous areas

waveform inversion for three dimensional density and s wave structure long period seismic data longer than about 100 s are sensitive to density as well as p wave and s wave structure in the earth seismograms containing overtone and fundamental mode signals are inverted directly for density and s wave velocity structure a simple relation between p wave and s wave velocity perturbations is assumed in order to reduce the number of unknowns a model is parameterized by spherical harmonics up to degree and order 8 and by five knots in depth at 30 220 450 670 and 882 km with linear interpolation between adjacent knots density resolution is good only at shallow depths in fact only the average in the upper 200 km is marginally resolved s wave resolution is generally good throughout the depth range s wave results show good correlation to surface geological features and are similar to previous studies density results show quite different patterns from s wave maps high density regions appear along the subduction zones surrounding the pacific ocean and low density regions appear in most major continents most continents have low density and high s wave velocity which suggests that continental mantle consists of compositionally different materials since thermal effects can never produce such perturbations high s wave velocity also suggests a relatively cold geotherm for continents and thus continents should consist of significantly low density material such as depleted mantle rocks as proposed by many researchers before the density map also correlates well with a geoid map for spherical harmonic components l 4 6 but not for l 2 3 it suggests that sources for these geoid undulations l 4 6 are in the upper mantle probably in the upper 300 400 km but those for l 2 3 are in deeper regions

the geoscience laser altimetry ranging system the geoscience laser altimetry ranging system glars is a planned highly precise laser distance measuring system to be used for geoscience measurements requiring extremely accurate geodetic observations from a space platform the system combines the attributes of a pointable laser ranging system making observations to retroreflectors placed on the ground with those of a nadir looking laser altimeter making height observations to ground ice sheet and oceanic surfaces in the ranging mode centimeter level precise baseline and station coordinate determinations will be made on grids consisting of 100 to 200 targets separated by distances from a few tens of kilometers to about 1000 km these measurements will be used for studies of seismic zone crustal deformations and tectonic plate motions ranging measurements will also be made to a coarser but globally distributed array of retroreflectors for both precise geodetic and orbit determination applications in the altimetric mode relative height determinations will be obtained with approximately decimeter vertical precision and 70 100 m horizontal resolution altimetric profiles consisting of nearly contiguous spots will be available when the system is operated at 40 pulses per second the height data will be used to study surface topography and roughness ice sheet and lava flow thickness and ocean dynamics waveform digitization will provide a measure of the vertical extent of topography within each footprint

gravity field of venus at constant altitude and comparison with earth the acceleration gravity anomaly estimates by spacecraft tracking determined from doppler residuals are components of the gravity field directed along the spacecraft earth line of sight los these data constitute a set of vector components of a planet s gravity field the specific component depending upon where the earth happened to be at the time of each measurement and they are at varying altitudes above the planet surface from this data set we have solved for the gravity field using the method of harmonic splines which imposes a smoothness criterion to select a gravity model compatible with the los data maps of geoid and gravity at spacecraft and at constant altitudes are presented for the planet venus for venus the major geoid and gravity anomalies each coincide spatially with the locations of positive topographic features these anomalies at 300 km altitude have significantly greater magnitude than anomalies that on earth are coincident with topographic features another striking difference is that most of the major geoid anomalies on the earth do not coincide with locations of its largest topographic features including continents but are due to deep sources on venus major mass anomalies appear to be restricted principally to the surficial 200 km of the planet a substantially thicker crust on venus 70 80 km compared to the earth s 5 40 km can explain its greater range of gravity anomaly and the positive correlation of gravity anomaly withtopographic height four regions with high gravity to topography response functions are interpreted to be due to crustal loading by recent volcanism perhaps combined with regional elevation of surface topography by thermal expansion from heating at depth

the migration of plate boundaries in se sicily influence on the large scale kinematic model of the african promontory in southern italy abstract a detailed field mapping coupled with structural analyses and morphological investigation has been carried out along the northern and western borders of the hyblean plateau se sicily in order to define the nature and the kinematics of a major quaternary fault belt this here designed as the scicli line fault belt is composed of two n50 oriented extensional basins that linked by a regional n10 trending transfer zone originated during the early pleistocene and experienced since the late quaternary a positive tectonic inversion in both the two stages of deformation the scicli line fault belt has been characterised by displacement rate comparable with the relative velocities measured between the distinct plates composing the central mediterranean region in the period going from 1 5 1 2 to 0 85 ma the fault belt accommodated the entire divergence between adria and nubia at present the scicli line fault belt absorbs most of the nubia eurasia convergence while the western divergent margin of the adria microplate has jumped to the eastern and the southern margins of the hyblean plateau along the late quaternary siculo calabrian rift zone the off shore prolongation of the two tectonic boundaries of the hyblean plateau has been recognised in the sicily channel where they are both interrupted by a wnw ese oriented dextral fault according to our reconstruction the hyblean plateau represents an isolated lithospheric block whose evolution can be related to the propagation of the western divergent margin of the adria microplate accompanied with the southward migration of the triple junction between eurasia nubia and adria in this new large scale kinematic picture the gps velocity measured in the hyblean region at the permanent site of noto is actually representative of the local kinematics rather than of the entire african promontory of southern italy this implies a correction of previous regional kinematic models based on combination of gps vectors in particular our data constrain a new interpretation both for the kinematics along the e w oriented nubia eurasia margin dominated by prevalent dextral deformation rather than reverse motions and for the intraplate deformation in the sicily channel within the africa promontory which would be dominated by a roughly n110 oriented extension this conclusion has implication also on the mechanism and the origin of the pantelleria linosa malta rift that is here interpreted as a transtensive feature developed along a major transform fault rather than the result of passive rifting induced by the nubia eurasia collision as it is currently interpreted

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

residual geoid anomalies in atlantic ocean basin relationship to mantle plumes the relations of geoid data from radar altimeter measurements geos 3 to water depth and geochemical variations along the mid atlantic ridge are investigated eight geophysical lines across the ridge in the atlantic ocean were constructed approximately normal to the local ridge trend slopes of geoid per kilometer of topographic relief show an asymmetry between the two sides of the ridge that generally is not matched by topography which has better symmetry between the two flanks subtracting a regional field based on previous work produces residual geoid anomalies whose source must be in the earth s outer 600 km the residual geoid anomalies of the north atlantic show striking correlation with the axis of the mid atlantic ridge but those in the south atlantic do not instead major positive residual geoid anomalies appear over the rio grande and walvis ridges determination of slope s residual geoid per million years crustal age reveals that s increases with greater residual geoid anomaly and with higher shallower crestal ridge topography the slope of 22 cm m y west of the azores high near 38 n suggests that the anomalously high crestal residual geoid and depth anomalies may not be entirely of thermal origin which may normally produce slopes only of about 8 cm m y as found near 28 n away from shallow ridge topography to account for this difference in slopes simply by a variation in mantle temperature would require a difference of about 940 c between the two sites which appears excessive also the decrease in topographic height with crustal age away from the azores high is much greater than predicted by theoretical cooling curves correlation of residual geoid anomalies with depth geochemical variations along the length of the mid atlantic ridge and the chemistry of the rio grande rise and walvis ridge suggest that many regions of anomalous residual geoid and crestal depth values may be in large part a function of crustal thickness and density variations induced by plume intrusion and volcanism in addition to their transient thermal effects

a global geodetic reference frame from lageos ranging sl5 1ap a summary of the results obtained for a new comprehensive geodetic parameter solution from the analysis of lageos laser ranging data for the period may 1976 to the end of 1982 is presented estimates of each component of the polar motion and earth rotation the station coordinates the value of the earth s gravitational constant gm and the elements of the lageos orbit comprise this sl5 1ap solution the results differ from previously published values primarily through incorporation of more rigorous dynamic models for the ocean and solid earth tides the precision of the geodetic parameters are on average 5 marc sec polar motion 0 2 ms length of day better than 5 cm center of mass geodetic positioning 3 cm global baselines and 2 cm regional baselines an assessment of the contribution of systematic errors in the interstation distance determination is presented

geological and geodetic constraints on the active deformation along the northern margin of the hyblean plateau se sicily abstract a geologic and geodetic integrated analysis of the northern margin of the hyblean plateau se sicily has been carried out in order to test the relationship between the active deformation recorded by gps data and the long term tectonic evolution reconstructed by the interpretation of structural and morphological data our study revealed the active growth of a large antiform as a consequence of the positive tectonic inversion of the previous flexure bordering the hyblean foreland the deformation of middle late pleistocene marine terraces and the evolution of the drainage system are consistent with a progressive regional tilting of the entire eastern sector of the hyblean plateau siracusa domain representing the southern limb of the active antiform the geometry of the late quaternary marine strandlines compared with the results of analogue models is compatible with the effects of the nw ward propagation of a detachment fault at depth the active deformation of the hyblean region coherent with the nubia eurasia plate convergence suggests to candidate the inverted tectonics at the northern border of the hyblean plateau as potential seismogenic sources of the area