Results from combining tectonic observations and SAR interferometry for the 1995 Grevena earthquake: A summary     

B. Meyer  R. Armijo  D. Massonnet  J. B. De Chabalier  C. Delacourt  J. C. Ruegg  J. Achache  D. Papanastassiou 《Journal of Geodynamics》1998,26(2-4)

Soon after the 1995 Grevena M_s = 6.6 event, we mapped the Palaeochori earthquake fault break. These tectonic observations are combined with the surface displacement field determined with the SAR interferometry to model the fault dislocation at depth.  相似文献   

Microdeformation of lacustrine laminite sequences from Late Miocene formations of SE Spain: an interpretation of loop bedding   总被引：2，自引：0，他引：2  

Jose P. Calvo  Miguel Rodriguez-Pascua  Silvia Martin-Velazquez  Sergio Jimenez  & Gerardo De Vicente 《Sedimentology》1998,45(2):279-292

Lacustrine laminated sediments (laminites) present in Late Miocene formations of the Híjar Basin, SE Spain, display well developed loop bedding, a structure consisting of bundles of laminae that are sharply constricted at intervals, giving a morphology of loops or links of a chain. The laminite sequences, which are interbedded with turbidite marlstones, were accumulated on the bottom of a permanently stratified lake developed in a rapidly subsiding basin limited by 010° and 105° normal faults. As deduced from both macro- and microdeformational analyses, the basin evolved under an extensional stress field throughout the Late Miocene. Four main types of loops, simple and complex loops with subcategories, have been recognized within the laminite sequence. Simple loops of type 1 show the best definite pattern, quite similar to ' pinch and swell structures ', a type of boudinage typical of stretching of alternating beds where the competence contrast is not strongly marked. The remaining loop types display contortion and occasional breakage of laminae (microfaulted edges) indicative of microdeformation near the boundary between the ductile-brittle deformational fields. The distribution of the various loop types across the laminite sequence reflects an interplay between progressive lithification of the laminites as sedimentation progressed and tectonic stresses which affected the sediment sequence. Accordingly, a mechanism of deformation under an extensional stress field, ultimately related to the creep movement of the main basin faults which resulted in successive seismic shocks of low magnitude, is proposed to explain the formation of loop bedding in the laminites.  相似文献   

Electronic and magnetic properties of a natural aegirine as observed from its Mössbauer spectra     

E. De Grave  A. Van Alboom  S. G. Eeckhout 《Physics and Chemistry of Minerals》1998,25(5):378-388

A natural sample of aegirine, ideally NaFeSi₂O₆, has been studied by transmission Mössbauer spectroscopy in the range 4.2–480?K. At selected temperatures, a longitudinal external field of 60?kOe was applied to the absorber. The sample was observed to order magnetically at 11±1?K. The paramagnetic Mössbauer spectra (MS) show the presence of ～10% Fe²⁺ in the M1 sites of the clinopyroxene structure. These MS have been decomposed into four quadrupole doublets: two minor ones for Fe²⁺ on M1 sites, a dominant one due to Fe³⁺ on M1 sites, and a second ferric component, with a contribution of ～3% and attributable to the tetrahedral sites. Two possibilities concerning the origin of the two distinct Fe²⁺ (M1) doublets are discussed. They are respectively based on inter-valence charge transfer and on the existence of distinct Fe²⁺ orbital configurations at the two M1 sites. Neither of the two models could be firmly excluded. The asymmetry parameter η of the electric field gradient at the Fe³⁺ (M1) sites is close to 1.0 and the quadrupole splitting within 0.34±0.01?mm/s at all temperatures. The MS at 4.2?K shows an asymmetric hyperfine-field distribution for Fe³⁺, with a maximum-probability field of 468?kOe. The maximum-probability field for Fe²⁺ is found to be 220?kOe. The shape of the applied-field MS at 4.2?K implies a static antiferromagnetic ordering and was successfully interpreted by a bidimensional distribution of the magnitude and orientation of the hyperfine field. Finally, the temperature variations of the respective centre shifts and quadrupole splittings could be explained on the basis of existing theoretical models.  相似文献   

Extragalactic source counts and contributions to the anisotropies of the cosmic microwave background: predictions for the Planck Surveyor mission     

Toffolatti  Argüeso Gómez  De Zotti  Mazzei  Franceschini  Danese  & Burigana 《Monthly notices of the Royal Astronomical Society》1998,297(1):117-127

We present predictions for the counts of extragalactic sources, the contributions to fluctuations and their angular power spectrum in each channel foreseen for the Planck Surveyor (formerly COBRAS/SAMBA ) mission. The contribution to fluctuations owing to clustering of both radio and far-IR sources is found to be generally small in comparison with the Poisson term; however the relative importance of the clustering contribution increases and may eventually become dominant if sources are identified and subtracted down to faint flux limits. The central Planck frequency bands are expected to be 'clean': at high galactic latitude (| b | > 20°), where the reduced galactic noise does not prevent the detection of the extragalactic signal, only a tiny fraction of pixels is found to be contaminated by discrete extragalactic sources. Moreover, the 'flat' angular power spectrum of fluctuations resulting from extragalactic sources substantially differs from that of primordial fluctuations; therefore, the removal of contaminating signals is eased even at frequencies where point sources give a sizeable contribution to the foreground noise.  相似文献   

Quantitative classification of WC and WO stars     

Crowther  Orsola De Marco  & Barlow 《Monthly notices of the Royal Astronomical Society》1998,296(2):367-378

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Effect of Spectral Resolution on the Mg II Index as a Measure of Solar Variability     

Oran R. White  Giuliana De Toma  Gary J. Rottman  Thomas N. Woods  Barry G. Knapp 《Solar physics》1998,177(1-2):89-103

The solar Mgii core-to-wing ratio is a useful index of UV variability throughout the solar cycle because it has been measured since 1978 in a series of successive satellite missions: Nimbus 7, Solar Mesosphere Explorer (SME), the NOAA 9–14 series, Upper Atmosphere Research Satellite (UARS), and ERS-2. Eventual construction of a single time series from 1978 to the present by combining these measurements will give a long record of almost daily UV variability to serve as a surrogate for estimating both UV and EUV solar radiation. Here we address the effect of spectral resolution on determination of both long-term and short-term solar variability from this index. We use UARS/SOLSTICE measurements of the Mgii line from October 1991 to December 1996 to study the effect of two spectral resolution regimes characteristic of existing measurements, 0.20 to 0.25 nm and 1.10 to 1.15 nm, on determination of the amplitude of 27-day rotational modulation and the more gradual change in chromospheric radiation in the declining phase of solar cycle 22. The two Mgii indices give solar variations that differ by a scaling factor of 2× for both the solar cycle change from 1992 to 1997 and the amplitude of 27-day modulation over the same period. Both types of measurements appear to yield solar signal equally well except at solar minimum when the solar changes become quite small.  相似文献   

Effect of hydrologic management on marsh surface sediment deposition in coastal Louisiana     

Denise J. Reed  Nina De Luca  A. Lee Foote 《Estuaries and Coasts》1997,20(2):301-311

High rates of coastal land loss in Louisiana have prompted efforts to maintain or restore coastal wetland habitats, and structural management of marsh hydrology is one of a number of approaches that has been adopted. The aim of this study was to determine the effect of hydrologic management measures on marsh-surface sediment deposition in the Mississippi deltaic plain. Four impoundments, ranging in size from 50 ha to 177 ha and similarly sized control sites were included in the study. At each site, marsh-surface sediment traps were collected approximately biweekly for 3.5 yr to measure changes in sediment deposition. There was no significant difference in sediment deposition between any of the impoundment and control sites during the premanagement period. The results show no significant difference in marsh-surface sediment deposition between management year 1992–1993 and management year 1994–1995, but management year 1993–1994 had significantly lower sediment deposition than either the first or the last year of the study. Management year 1992–1993 showed the highest sediment deposition when it was assessed across all basins, areas, and sites, and this high rate of deposition is accounted for by the impact of Hurricane Andrew. For all management years there were significant differences between impoundment and control sites, with control sites showing higher rates of marsh surface sediment deposition than impoundments. No clear pattern was identified concerning the influence of various types of hydrologic management on rates of sediment deposition. This reduction in sediment deposition indicated that the areas under management in this study are receiving insufficient inorganic sediment deposition to keep pace with sea-level rise.  相似文献   

Warming at 18,000 yr B.P. in the Tropical Andes     

Karin F. Helmens  Peter Kuhry  Nathaniel W. Rutter  Klaas Van Der Borg  Arie F. M. De Jong 《Quaternary Research》1996,45(3):289-299

Palynological, paleopedological, and glacial geomorphological evidence from the area of the high plain of Bogotá in the Colombian Eastern Cordillera indicates a significant climatic warming around 18,000¹⁴C yr B.P. Comparison of dated vegetation changes, pedogenic episodes, and glacier fluctuations provides the basis for defining the so-called “La Laguna Interstadial” that lasted from 19,500 to 17,000 yr B.P. During this interstadial period, mean annual temperatures in the tropical Andes were up to 4°C higher than during the preceding and following stadial periods, when full-glacial conditions prevailed and temperatures were up to 8°C colder than at present.  相似文献   

Modelling of ground acceleration in the near source range: the case of 1976, Friuli earthquake (M = 6.5), northern Italy     

Aldo Zollo  Antonella Bobbio  Antonio Emolo  André Herrero  Giuseppe De Natale 《Journal of Seismology》1997,1(4):305-319

A mixed statistical-deterministic model of earthquake rupture is developed for evaluating the strong ground motion in the near source range (receiver distance comparable to the fault length). The source parametrization is based on the k-square model and the propagation is computed by asymptotic Green's functions. The method is applied to the case of 1976, Friuli earthquake (M = 6.5) in northern Italy which occurred on a low-dip thrusting fault. Acceleration records at 29 stations are computed for 100 simulations of rupture histories. The mean value map of peak ground accelerations shows clearly a maximum to the south due to the inner geometry and directivity of the source. The variation of the estimated PGA versus the epicentral distance is strongly dependent on azimuth and is not decreasing monotonically. The comparison of these curves with those predicted by empirical acceleration–distance relationships shows discrepancies in the near source distance range. This study shows the importance of considering the complexity of the source rupture process for strong motion estimate in the near source range.  相似文献   

Constraints on the shallow crustal model of the Northern Apennines (Italy) from the analysis of microearthquake seismic records   总被引：1，自引：0，他引：1  

Aldo Zollo  Raffaella De Matteis  Paolo Capuano  Flora Ferulano  Giovanni Iannaccone 《Geophysical Journal International》1995,120(3):646-662

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