A double seismic antenna experiment at teide Volcano: existence of local seismicity and lack of evidences of Volcanic tremor     

J. Almendros  J. M. Ibez  G. Alguacil  J. Morales  E. Del Pezzo  M. La Rocca  R. Ortiz  V. Araa  M. J. Blanco 《Journal of Volcanology and Geothermal Research》2000,103(1-4)

Data analyzed in the present work correspond to a 40 days field experiment carried out in Teide Volcano (Canary Islands, Spain) with two short-period small-aperture dense seismic antennas in 1994. The objective of this experiment was to detect, analyze and locate the local seismicity. We analyzed also the background seismic noise to investigate the possible presence of volcanic tremor. From a set of 76 events, we selected 21 of them in base of their good signal-to-noise ratio and their possibility to locate their seismic source by using the seismic antennas. A visual classification based on the S–P time and seismogram shape has permitted to establish three groups of events: local seismicity (S–P time between 3 and 5 s), very local earthquakes (S–P time smaller than 3 s) and artificial explosions. These earthquakes have been located by applying the Zero Lag Cross-Correlation technique and the inverse ray-tracing procedure. Those earthquakes that were recorded simultaneously by both seismic antennas were also located by intersecting both back-azimuths. The analysis of the seismicity has revealed that the amount of seismicity in Teide Volcano is moderate. This seismicity could be distributed in three main areas: inside the Caldera Edifice (below the Teide–Pico Viejo complex), in the eastern border of the Caldera Edifice and offshore of the island. At present, this activity is the only indicator of the volcano dynamics. The analysis of the back-ground seismic noise has revealed that at frequencies lower than 2 Hz, the Oceanic Load signal is predominant over other signals, even over local earthquakes with a magnitude of 2.0. Due to this, although if in the Teide area were present a weak volcanic tremor, or other volcanic signals with predominant peaks below 2 Hz, to observe them would be a very difficult task.  相似文献   

Source mechanism and surface wave excitation for two earthquakes in northern Baja California, Mexico     

F. Alejandro Nava  James N. Brune 《Geophysical Journal International》1983,73(3):739-763

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Magnetoacoustic surface gravity waves     

Alejandro G. González  Julio Gratton 《Solar physics》1991,134(2):211-232

The effect of gravity on the surface magnetoacoustic waves may be important when considering applications to solar and laboratory plasmas. The linear magnetoacoustic waves, which may appear in a configuration with an interface between two plasmas or a plasma and an ordinary gas, are studied. Compressibility and gravity are taken into account. The different types of couplings between internal and surface modes are analyzed. Magnetoacoustic surface waves are studied in detail in a configuration consisting of an interface between an isothermal plasma and an ordinary gas. The possible regions where these modes may exist are discussed. A general way of grouping and classifying the complicated spectra of modes is presented. New groups of modes appear as a consequence of gravity and stratification, in addition to those already present in the absence of gravity. The results may be of help in studying more complicated cases.Researcher of the Consejo Nacional de Investigaciones Científicas y Técnicas.  相似文献   

The airborne transport of Saharan dust: A review     

Christer Morales 《Climatic change》1986,9(1-2):219-241

The extent of the short and long-range transport, and the atmospheric residence time of airborne Saharan dust are dependent on factors like the initial size distribution of the dust and the type of weather systems raising dust and creating different kinds of dust storms.The paper discusses these factors. It further reviews a number of investigations of long-range transport of Saharan dust out from the Sahara, and shows how eolian dust can be monitored with the help of meteorological SYNOP and METAR observations.  相似文献   

A note on spectral evaluation at the Nyquist frequency     

F. Alejandro Nava 《Pure and Applied Geophysics》1983,121(5-6):913-916

The determination of the spectral component of a signal corresponding to the Nyquist frequencyf _N is not reliable. A rule is proposed to determine the highest reliable frequencyf _R for a given sampling rate Δt and time windowN Δt (whereN is the total number of samples) asf _R=f _N(1?1/2N).  相似文献   

The Oyambre coastal terrace: a detailed sedimentary record of the Last Interglacial Stage in northern Iberia (Cantabrian coast,Spain)     

Elisa Sainz de Murieta  Pedro P. Cunha  Alejandro Cearreta  Andrew S. Murray  Jan-Pieter Buylaert 《第四纪科学杂志》2021,36(4):570-585

A detailed study is presented of a 15.3-m-thick Pleistocene coastal terrace located on the Cantabrian coast (northern Spain). Stratigraphic, sedimentological, topographic and micropalaeontological information is combined with a chronology based on luminescence dating to characterize the deposits. The sedimentary succession records: (i) a basal transgressive system, consisting of a wave-cut surface covered by a lower layer of beach gravels and upper beach pebbly sands; and (ii) a thicker upper highstand system (aggrading), comprising medium to very fine aeolian sands interbedded with thin palustrine muds. Luminescence dating involved a detailed sampling strategy (36 samples and two modern analogues) and the use of both quartz optically stimulated luminescence (OSL) and feldspar post-infrared infrared stimulated luminescence single aliquot regeneration protocols; feldspar results were used to confirm the completeness of bleaching of the quartz OSL signal. The quartz OSL luminescence age–depth relationship shows significant dispersion, but nevertheless two rapid phases of deposition can be clearly identified: one at ~130 ka [Marine Oxygen Isotope Stage (MIS) 5] and one at ~100 ka (MIS 5c). The top of the succession is dated to ~70 ka. The MIS 5e marine maximum flooding surface is identified at an elevation of 6.85 m above mean seal level. This elevation provides evidence of a regional sea-level highstand for this sector of the Cantabrian coast.  相似文献   

Grazing effects on patchy dryland vegetation in northern Patagonia   总被引：1，自引：0，他引：1  

Alejandro J Bisigato  Mónica B Bertiller 《Journal of Arid Environments》1997,36(4):639-653

In this study the spatial patterns and dynamics of vegetation patches along a grazing gradient in the steppe ofLarrea divaricataandStipaspp. in NE Patagonia (Argentina) are described. A general effect of grazing is the reduction of total plant cover resulting from the decrease in cover of perennial grasses (Stipa speciosa, Poa ligularis, Stipa tenuis) and some tall shrubs (Chuquiraga hystrix, Bougainvillea spinosa, Lycium chilense). Dwarf shrubs (Nassauvia fueguianaandJunellia seriphioides) increase their cover under medium and/or high grazing pressures. Plant species are spatially grouped into patches which alternate with areas of bare soil. Eleven types of vegetation patch differing in the dominant plant functional type or species, floristic richness and size were identified with different relative frequency along the grazing gradient. Based on these results, it is postulated that grazing forces the replacement of large patches dominated by tall shrubs with high species richness, byLarrea divaricatapatches or small dwarf shrub patches with low species richness and the extinction of grass patches. This results from: (1) disruption of local balances of species deletions and additions; (2) fragmentation of large patches; and (3) formation of new vegetation patches. These changes lead to differing plant spatial organization and heterogeneity along the grazing gradient which may be described by characteristic arrays of vegetation patches.  相似文献   

The use of higher taxa to assess the benthic conditions in the southern Gulf of Mexico     

Nayeli Domínguez-Castanedo  Ricardo Rojas-López  Vivianne Solís-Weiss  Pablo Hernández-Alcántara  & Alejandro Granados-Barba 《Marine Ecology》2007,28(S1):161-168

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Demersal trawling waste as a food source for Western Mediterranean seabirds during the summer     

Martinez-Abrain  Alejandro; Maestre  Raquel; Oro  Daniel 《ICES Journal of Marine Science》2002,59(3):529-537

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A synthesis of the early life history of the anglerfish, Lophius piscatorius (Linnaeus, 1758) in northern British waters   总被引：1，自引：0，他引：1  

Hislop  John R.G.; Gallego  Alejandro; Heath  Michael R.; Kennedy  Fiona M.; Reeves  Stuart A.; Wright  Peter J. 《ICES Journal of Marine Science》2001,58(1):70-86

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