RESPONSE SPECTRA FOR DIFFERENTIAL MOTION OF COLUMNS     

MIHAILO D. TRIFUNAC  MARIA I. TODOROVSKA 《地震工程与结构动力学》1997,26(2):251-268

The validity of the response spectrum concept for determining loads in structures excited by differential earthquake ground motion is examined. It is shown that the common definition of response spectrum for synchronous ground motion can be reconciled to remain valid in cases when the columns of extended structures experience different motions. Then, a relative displacement response spectrum for design of first-storey columns, SDC(T, δ, ζ, τ), is defined. In addition to natural period, T, and fraction of critical damping, ζ, this spectrum depends also on the ‘travel time’, τ (of the waves in the soil over distances about one half width, or length of the structure), and on a factor, δ, specifying the relative displacement of the first floor. It is shown how this spectrum can be determined using existing empirical scaling equations for relative displacement spectra SD(T, ζ) and for peak velocity and peak acceleration of strong ground motion. These new spectra are illustrated for a horizontal component of a record in the near field of the 1994 Northridge earthquake. The results show that differential motions are more important for short period (stiff) than for longer period (flexible) structures, and for structures founded on softer ground (small shear wave velocity). © 1997 by John Wiley & Sons, Ltd.  相似文献   

Phase partitioning for different aerosol species in fog   总被引：2，自引：0，他引：2  

A. HALLBERG  J. A. OGREN  K. J. NOONE  J. HEINTZENBERG  A. BERNER  I. SOLLY  C. KRUISZ  G. REISCHL  S. FUZZI  M. C. FACCHINI  H.-C. HANSSON  A. WIEDENSOHLER  I. B. SVENNINGSSON 《Tellus. Series B, Chemical and physical meteorology》1992,44(5):545-555

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Association of tepees and palaeokarst in the Ladinian Calcare Rosso (Southern Alps, Italy)   总被引：1，自引：0，他引：1  

MARIA MUTTI 《Sedimentology》1994,41(3):621-641

The Ladinian Calcare Rosso of the Southern Alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst. This unit comprises peritidal strata pervasively deformed into tepees, repeatedly capped by palaeokarst surfaces mantled by terra rossa. Palaeokarsts, characterized by a regional distribution across the Southern Alps, occur at the base and at the top of the unit. Local palaeokarsts, confined to this part of the platform, occur within the Calcare Rosso and strongly affected depositional facies. Tepee deformation ranges from simple antiformal structures (peritidal tepees) to composite breccias floating in synsedimentary cements and internal sediments (senile tepees). Peritidal tepees commonly occur at the top of one peritidal cycle, in association with subaerial exposure at the cycle top, while senile tepees affect several peritidal cycles, and are always capped by a palaeokarst surface. Cements and internal sediments form up to 80% of the total rock volume of senile tepees. The paragenesis of senile tepees is extremely complex and records several, superimposed episodes of dissolution, cement precipitation (fibrous cements, laminated crusts, mega-rays) and deposition of internal sediments (marine sediment and terra rossa). Petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions, ranging from marine to meteoric, and were altered soon after precipitation in the presence of either meteoric or mixed marine/meteoric waters. Stable isotope data for the cements and the host rock show the influence of meteoric water (average δ¹⁸O= - 5·8‰), while strontium isotopes (average ⁸⁷Sr/86Sr=0·707891) indicate that cements were precipitated and altered in the presence of marine Triassic waters. Field relationships, sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting. Senile tepees formed in a karst-dominated environment in the presence of extensive meteoric water circulation, in contrast to previous interpretations that tepees formed in arid environments, under the influence of vadose diagenesis. Tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up-buckling of strata. This porosity acted as a later conduit for either meteoric or mixed marine/meteoric fluids, when a karst system developed in association with prolonged subaerial exposure. Relative sea level variations, inducing changes in the water table, played a key role in exposing the peritidal cycles to marine, mixed marine/meteoric and meteoric diagenetic environments leading to the formation of senile tepees. The formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression, punctuated by different orders of sea level variations, which allowed formation and later freezing of the cave infills.  相似文献   

Palaeowind directions recorded in the youngest loess in Poland and western Ukraine as derived from anisotropy of magnetic susceptibility measurements     

JERZY NAWROCKI  OLGA POLECHOSKA  REJ BOGUCKIJ  MARIA &#;ANCZONT 《Boreas: An International Journal of Quaternary Research》2006,35(2):266-271

Studies of the anisotropy of magnetic susceptibility (AMS) were carried out in order to define the directions and strength of palaeowind during the sedimentation of the youngest loesses in Poland and western Ukraine. These sediments, like the Chinese and Alaskan loesses, appear suitable for application of the AMS method. The inclined mean minimum axes were considered as reflecting the prevailing palaeowind direction at the time of loess sedimentation. The majority of the sections studied indicate a palaeowind direction from W-SW to E-NE, with a mean azimuth of 258°. This direction corresponds to the strike of the Weichselian ice-sheet margin and is parallel to the axis of the lowland between the ice-sheet margin to the north and the Carpathian Mountains and the Podole Upland to the south. Further AMS studies of the oldest parts of loess sequences in Poland and western Ukraine may help in reconstruction of the atmospheric circulation in this part of Europe since c. 900 kyr BP.  相似文献   

Kilauea East Rift Zone Magmatism: an Episode 54 Perspective   总被引：1，自引：0，他引：1  

THORNBER  CARL R.; HELIKER  CHRISTINA; SHERROD  DAVID R.; KAUAHIKAUA  JAMES P.; MIKLIUS  ASTA; OKUBO  PAUL G.; TRUSDELL  FRANK A.; BUDAHN  JAMES R.; RIDLEY  W. IAN; MEEKER  GREGORY P. 《Journal of Petrology》2003,44(9):1525-1559

On January 29–30, 1997, prolonged steady-state effusionof lava from Pu'u'O'o was briefly disrupted by shallow extensionbeneath Napau Crater, 1–4 km uprift of the active Kilaueavent. A 23-h-long eruption (episode 54) ensued from fissuresthat were overlapping or en echelon with eruptive fissures formedduring episode 1 in 1983 and those of earlier rift zone eruptionsin 1963 and 1968. Combined geophysical and petrologic data forthe 1994–1999 eruptive interval, including episode 54,reveal a variety of shallow magmatic conditions that persistin association with prolonged rift zone eruption. Near-ventlava samples document a significant range in composition, temperatureand crystallinity of pre-eruptive magma. As supported by phenocryst–liquidrelations and Kilauea mineral thermometers established herein,the rift zone extension that led to episode 54 resulted in mixtureof near-cotectic magma with discrete magma bodies cooled to  相似文献   

Phytoplankton dynamics in the Barents Sea estimated from chlorophyll budget models   总被引：1，自引：0，他引：1  

MARIA VERNET 《Polar research》1991,10(1):129-146

Pigment budgets use chlorophyll a and phaeopigment standing stock in combination with their photo-oxidation and sedimentation rates in the euphotic zone to estimate phytoplankton growth and grazing by micro- and macrozooplankton. Using this approach, average phytoplankton growth in the euphotic zone of the Barents Sea was estimated at 0.17 and 0.14 d⁻¹ during spring of 1987 and 0.018 and 0.036 d⁻¹ during late- and postbloom conditions in summer of 1988. Spring growth was 65% lower than the estimates from radiocarbon incorporation, supporting a 33% pigment loss during grazing. Macrozooplankton grazing and cell sinking were the main loss terms for phytoplankton during spring while microzooplankton grazing was dominant in summer.
In contrast to tropical and temperate waters, Arctic waters are characterized by a high phaeopigment: chlorophyll a ratio in the seston. Photooxidation rates of phaeopigments at in situ temperatures (0 ± 1°C) are lower than in temperate waters and vary by a factor of 2 for individual forms (0.009 to 0.018 m⁻²mol⁻¹). The phaeopigment fraction in both the suspended and sedimenting material was composed of seven main compounds that were isolated using high-performance liquid chromatography and characterized by spectral analysis. The most abundant phaeopigment in the sediment traps, a phaeo-phorbide-like molecule of intermediate polarity (phaeophorbide a₃), peaked in abundance in the water column below the 1% isolume for PAR (60-80 m) and showed the highest rate of photooxidation. This phaeopigment was least abundant in the seston when phytoplankton was dominated by prymnesiophytcs but increased its abundance in plankton dominated by diatoms. This distribution suggests that larger grazers feeding on diatoms are the main producers of this phaeopigment.  相似文献   

Capturing and modelling metre‐scale spatial facies heterogeneity in a Jurassic ramp setting (Central High Atlas,Morocco)     

FRÉDÉRIC AMOUR  MARIA MUTTI  NICOLAS CHRIST  ADRIAN IMMENHAUSER  SUSAN M. AGAR  GREGORY S. BENSON  SARA TOMÁS  ROBERT ALWAY  LACHEN KABIRI 《Sedimentology》2012,59(4):1158-1189

Each simulation algorithm, including Truncated Gaussian Simulation, Sequential Indicator Simulation and Indicator Kriging is characterized by different operating modes, which variably influence the facies proportion, distribution and association of digital outcrop models, as shown in clastic sediments. A detailed study of carbonate heterogeneity is then crucial to understanding these differences and providing rules for carbonate modelling. Through a continuous exposure of Bajocian carbonate strata, a study window (320 m long, 190 m wide and 30 m thick) was investigated and metre‐scale lithofacies heterogeneity was captured and modelled using closely‐spaced sections. Ten lithofacies, deposited in a shallow‐water carbonate‐dominated ramp, were recognized and their dimensions and associations were documented. Field data, including height sections, were georeferenced and input into the model. Four models were built in the present study. Model A used all sections and Truncated Gaussian Simulation during the stochastic simulation. For the three other models, Model B was generated using Truncated Gaussian Simulation as for Model A, Model C was generated using Sequential Indicator Simulation and Model D was generated using Indicator Kriging. These three additional models were built by removing two out of eight sections from data input. The removal of sections allows direct insights on geological uncertainties at inter‐well spacings by comparing modelled and described sections. Other quantitative and qualitative comparisons were carried out between models to understand the advantages/disadvantages of each algorithm. Model A is used as the base case. Indicator Kriging (Model D) simplifies the facies distribution by assigning continuous geological bodies of the most abundant lithofacies to each zone. Sequential Indicator Simulation (Model C) is confident to conserve facies proportion when geological heterogeneity is complex. The use of trend with Truncated Gaussian Simulation is a powerful tool for modelling well‐defined spatial facies relationships. However, in shallow‐water carbonate, facies can coexist and their association can change through time and space. The present study shows that the scale of modelling (depositional environment or lithofacies) involves specific simulation constraints on shallow‐water carbonate modelling methods.  相似文献   

Magnetic mineral transport and sorting in the swash‐zone: northern Lake Erie,Canada     

ERIC GALLAWAY  ALAN S. TRENHAILE  MARIA T. CIOPPA  ROBERT G. HATFIELD 《Sedimentology》2012,59(6):1718-1734

A combined field and laboratory study in northern Lake Erie has provided new insights into the origin and dynamics of heavy mineral placer deposits on beaches consisting primarily of non‐magnetic sediment. Work was conducted on the cross‐shore and longshore transport of heavy magnetic minerals using magnetic susceptibility and fluorescent paints to trace the movement, in the field, of samples of magnetic (magnetite) and non‐magnetic (quartz and calcite) grains, respectively. Laboratory experiments examined how the burial of small, dense magnetic minerals is affected by the grain size of the non‐magnetic host material, and how grain burial affects magnetic susceptibility measurements at the surface. The field experiments demonstrated that the magnetic mineral tracers were buried rapidly beneath coarser, non‐magnetic grains under low to moderate wave conditions, and subsequently were unable to move in the longshore or cross‐shore directions. The laboratory experiments showed that the magnetic susceptibility rapidly decreased with the rate and depth of burial of the magnetic minerals, and that magnetic grain burial was most effective beneath coarser rather than finer non‐magnetic sand and, for the latter sediments, under less rather than more energetic conditions. The results imply that magnetic mineral concentrations develop in this area through magnetic grain burial under fairly mild conditions, and subsequent settling, exposure and concentration in the upper swash zone during more energetic periods, when the non‐magnetic grains are eroded. It is probably during these erosional periods, when the magnetic minerals are exposed in fairly homogeneous deposits, that longshore and cross‐shore transport takes place.  相似文献