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371.
The algorithm CN makes use of normalized functions. Therefore the original algorithm, developed for the California-Nevada region, can be directly applied, without adjustment of the parameters, to the determination of the Time of Increased Probability (TIP) of strong earthquakes for Central Italy. The prediction is applied to the events with magnitudeMM
0=5.6, which in Central Italy have a return period of about six years. The routinely available digital earthquake bulletins of the Istituto Nazionale di Geofisica (ING), Rome, permits continuous monitoring. Here we extend to November 1994 the first study made by Keilis-Boroket al. (1990b). On the basis of the combined analysis of seismicity and seismotectonic, we formulate a new regionalization, which reduces the total alarm time and the failures to predict, and narrows the spatial uncertainty of the prediction with respect to the results ofKeilis-Borok
et al. (1990b).The premonitory pattern is stable when the key parameters of the CN algorithm and the duration of the learning period are changed, and when different earthquake catalogues are used.The anlysis of the period 1904–1940, for whichM
0=6, allows us to identify self-similar properties between the two periods, in spite of the considerably higher seismicity level of the earlier time interval compared with the recent one. 相似文献
372.
G. M. da Costa E. De Grave L. H. Bowen P. M. A. de Bakker R. E. Vandenberghe 《Physics and Chemistry of Minerals》1995,22(3):178-185
Synthetic aluminum-substituted maghemite samples, -(Al
y
Fe1-y
)2O3 with y=0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by Mössbauer spectroscopy at 8 K and in the range 80 K to 475 K at steps of 25 K. The spectra have been analysed as a superposition of two sextets composed of asymmetrical Lorentzians. The A- and B-site isomer shifts were constrained as: A=B-0.12 mm/s. From the temperature dependence of B it was possible to determine the characteristic Mössbauer temperature and the intrinsic shift. Both quantities clearly increase with increasing Al content, at least up to 10 mole%. The temperature dependence of the A-and B-sites hyperfine fields could be satisfactorily reproduced using the molecular-field theory assuming an antiparallel spin configuration. The exchange integrals were found as: J
AB
=-25 K; J
AA
=-18 K and J
BB
= -3 K. The hyperfine fields show a crossing in the vicinity of 300 K as a result of the relatively strong A-A interaction. The Curie temperature for the non-substituted sample was calculated to be 930 K and decreases to 765 K for the sample with 15 mol% Al. The gradual decrease of the saturation value of the A-site hyperfine field with increasing Al substitution and the constancy of this quantity for the B sites, suggest that the Al cations occupy the B sites.Research Director, National Fund for Scientific Research, Belgium 相似文献
373.
The impulsive solar burst of October 28, 1992 showed temporal and spatial fine structures that were observed at 48 GHz with the multi-beam antenna of the Itapetinga Radio Observatory. The relative positions of burst centroids were determined with a spatial accuracy of 2, with a temporal resolution of 1 millisecond. The burst intensity time profile shows fast pulses of about one second duration, superimposed by subsecond time structures. The spatial analysis of the fast pulses suggests that the emission originated from distinct locations, separated by about 5. Our results favour the idea that impulsive solar bursts are a superposition of small elementary events spread both in time and space, probably resulting from discontinuous energy release processes. 相似文献
374.
375.
The Caturrita Formation is a lithostratigraphic unit that comprises the Ladinian–Eonorian sequence of the Paraná Basin. It has been interpreted as deposits of alluvial plains and meandering rivers. Purported fossil tracks found in this formation at Faxinal do Soturno County, Rio Grande do Sul State, Brazil, are concave circular-shaped structures, with a laminar deformation. Some show digitiform projections, and at least three are aligned. They are interpreted as a disruption of the substrate homogeneity caused by bioturbation of tetrapods. In some of these there is a distinct color pattern — more reddish than the surrounding substrate. This is interpreted as a result of differential diagenesis. The features remain enigmatic tracks but were probably made by prosauropod dinosaurs, the dominant terrestrial herbivore group from the end of the Triassic in Gondwana strata. 相似文献
376.
In the English Channel, extreme surge heights did not occur at the time of extreme high tides during the last decades and
maximum recorded heights usually do not exceed the maximum astronomical tide by more than a few decimetres. To understand
whether this lack of coincidence may be due to specific phenomena or only to chance, we have studied hourly tide records lasting
a few decades from nine English and nine French stations as well as air pressure and wind data from nearby meteorological
observatories. Among the case studies of moderate flooding at several coastal stations occurring during spring tide, we have
selected those of 24–25/10/1980 and of 30/01/1983 to 02/02/1983 as representative of a normal situation without any special
chance. The third case study 26–28/02/1990 was potentially more dangerous because of the storm intensity and duration; however,
by chance, surge peaks occurred near the low tide. Finally, the propagation of the surge peak of 15–16/10/1987, which reached
the maximum height recorded during all the instrumental period at several stations, has been followed all along the English
Channel, using the hourly records of 12 tide-gauge stations and of 16 meteorological stations. The surge peak of this great
storm, probably the strongest in the last two centuries, occurred everywhere at high tide and spread with the same velocity
of the tidal wave. Fortunately, no major flooding occurred because it was the day after a neap tide. In conclusion, some good
fortune has saved the low coastal areas of the English Channel from major floods during the last decades. However, the occurrence
of the peak of a strong storm surge arriving near the western entrance of the Channel at the time of a great astronomical
high tide is a possible event that could be devastating along both sides of the Channel coasts.
Main parts of this paper have been presented orally in June 2005 at the joint INQUA–IGCP 495 Meeting “Dunkerque 2005” and
in February 2006 at the ASLO-TOS-AGU “Ocean Sciences Meeting” (Honolulu, HI). 相似文献
377.
John Douglas Hideo Aochi Peter Suhadolc Giovanni Costa 《Bulletin of Earthquake Engineering》2007,5(1):17-26
In this short article, the possible reduction in the standard deviation of empirical ground motion estimation equations through
the modelling of the effect of crustal structure is assessed through the use of ground-motion simulations. Simulations are
computed for different source-to-site distances, focal depths, focal mechanisms and for crustal models of the Pyrenees, the
western Alps and the upper Rhine Graben. Through the method of equivalent hypocentral distance introduced by Douglas et al.
[(2004) Bull Earthquake Eng 2(1): 75–99] to model the effect of crustal structure in empirical equations, the scatter associated
with such equations derived using these simulated data could be reduced to zero if real-to-equivalent hypocentral distance
mapping functions were derived for every combination of mechanism, depth and crustal structure present in the simulated dataset.
This is, obviously, impractical. The relative importance of each parameter in affecting the decay of ground motions is assessed
here. It is found that variation in focal depth is generally more important than the effect of crustal structure when deriving
the real-to-equivalent hypocentral distance mapping functions. In addition, mechanism and magnitude do not have an important
impact on the decay rate. 相似文献
378.
In the framework of the Catania Project supported by GNDT (Gruppo Nazionale per la Difesa dai Terremoti) seismic measurements have been carried out in the shore sands of Catania to define their detailed shear wave velocity (V) profiles and attenuation properties (Q). The method used, FTAN, is based on the analysis of the dispersion curve extracted from signals generated by controlled sources. The computation of complete synthetic seismograms enables the estimation of the attenuation properties of the surface layers. Hereinafter we analyse the shear seismic characteristics of the shore sands as indicators of potential liquefaction phenomena. 相似文献
379.
Pieter R. van Oel Eduardo S. P. R. Martins Alexandre C. Costa Niko Wanders Henny A. J. van Lanen 《水文科学杂志》2020,65(Z1):979-990
ABSTRACTTo effectively manage hydrological drought, there is an urgent need to better understand and evaluate its human drivers. Using the “downstreamness” concept, we assess the role of a reservoir network in the emergence and evolution of droughts in a river basin in Brazil. In our case study, the downstreamness concept shows the effect of a network of reservoirs on the spatial distribution of stored surface water volumes over time. We demonstrate that, as a consequence of meteorological drought and recovery, the distribution of stored volumes became spatially skewed towards upstream locations, which affected the duration and magnitude of hydrological drought both upstream (where drought was alleviated) and downstream (where drought was aggravated). The downstreamness concept thus appears to be a useful entry point for spatiotemporally explicit assessments of hydrological drought and for determining the likelihood of progression from meteorological drought to a human-modified hydrological drought in a basin. 相似文献
380.
Prof. Dr. Luis Alfredo Moutinho da Costa Prof. M. Sc. Antonio Gomes Angeiras 《International Journal of Earth Sciences》1971,60(3):1024-1050
Evidences of geosynclinal polarity (orogenic and sedimentary) in foldbelts of Central Brazil led the authors to the recognition of seven tectonic isopic zones as parts of a wide geosynclinal system policyclically developed during a long Baykalian Cycle of 1,500-500 m. y. ago. Tectonic and stratigraphic evolutions are reinterpreted on the light of the new concepts.The orogenic polarity of contiguous miogeosynclinal and eugeosynclinal foldbelts provided the basis for enlarging the Brasiliane Cycle of short duration (850–550 m. y.) to a Brasiliane Cycle of 1,500-550 m.y. (= Baykalian Cycle). The Minas Cycle is viewed as a phase within a distinct platform-making process.
Zusammenfassung Die PolaritÄt orogener und sedimentÄrer Erscheinungen in Geosynklinalen der Faltengürtel Zentralbrasiliens veranla\te die Autoren, sieben tektonische Zonen als Teile eines gro\rÄumigen geosynklinalen Systems, das wÄhrend eines langen Baykalischen Zyklusses vor 1500 bis 500 Millionen Jahren entstand, zu unterscheiden. Tektonische und stratigraphische Entwicklungen werden im Lichte dieser neuen Auffassung neu interpretiert.Die orogene PolaritÄt von aneinandergrenzenden miogeosynklinalen und eugeosynklinalen Faltengürteln lieferte die Grundlage für die Erweiterung des Brasilianischen Zyklusses von kurzer Dauer (850-550 Millionen Jahre) zu einem Brasilianischen Zyklus von 1500-500 Millionen Jahren (=Baykalischer Zyklus). Der Minas-Zyklus wird als eine Phase innerhalb eines Plattform bildenden Prozesses angesehen.
Résumé Certaines évidences de polarité géosynclinale (orogéniques et sedimentaires) dans les régions plissées du Brésil Central ont conduit les auteurs a établir sept zones tectoniques rassemblées dans un seul système géosynclinal, qui s'est développé policycliquement au cours d'un Cycle Baykalien de 1500 à 500 millions d'années. Les évolutions stratigraphiques et tectoniques sont réinterprétées à la lumière de nouveaux concepts.La polarité orogénique du couple eugéosynclinal-miogéosynclinal de ces zones plissées a fourni des données suffisantes pour étendre les limites du Cycle Brésilien (= Baykalien) de 850–550 millions d'années à 1500–550 millions d'années: le Cycle Minas est devenu simplement une phase dans ce processus de formation de plateformes.
7 , 1500-500 . . 850–500 1500-500 ( ). , .相似文献