Analysis of the weightiness of site effects on reinforced concrete (RC) building seismic behaviour: The Adra town example (SE Spain)   总被引：1，自引：0，他引：1  

Manuel Navarro  Francisco Vidal  Takahisa Enomoto  Francisco J. Alcalá  Antonio García‐Jerez  Francisco J. Sánchez  Norio Abeki 《地震工程与结构动力学》2007,36(10):1363-1383

The damage distribution in Adra town (south‐eastern Spain) during the 1993 and 1994 Adra earthquakes (5.0 magnitude), that reached a maximum intensity degree of VII (European Macroseismic Scale (EMS scale)), was concentrated mainly in the south‐east zone of the town and the most relevant damage occurred in reinforced concrete (RC) buildings with four or five storeys. In order to evaluate the influence of ground condition on RC building behaviour, geological, geomorphological and geophysical surveys were carried out, and a detailed map of ground surface structure was obtained. Short‐period microtremor observations were performed in 160 sites on a 100m × 100m dimension grid and Nakamura's method was applied in order to determine a distribution map of soil predominant periods. Shorter predominant periods (0.1–0.3 s) were found in mountainous and neighbouring zones and larger periods (greater than 0.5 s) in thicker Holocene alluvial fans. A relationship T = (0.049 ± 0.001)N, where T is the natural period of swaying motion and N is the number of storeys, has been empirically obtained by using microtremor measurements at the top of 38 RC buildings (ranging from 2 to 9 storeys). 1‐D simulation of strong motion on different soil conditions and for several typical RC buildings were computed, using the acceleration record in Adra town of the 1993 earthquake. It is noteworthy that all the aforementioned results show the influence of site effects in the degree and distribution of observed building damage. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Peralkaline acid tendencies in Gran Canaria (Canary Islands)     

Vicente Araña  Eduardo R. Badiola  Dr. Francisco Hernán 《Contributions to Mineralogy and Petrology》1973,40(1):53-62

The study of a volcanic series from the island of Gran Canaria (Canary Islands) in which alkaline and peralkaline, saturated and undersaturated rocks coexist, is reported here. Materials with high volatile content (ignimbritic trachytes) were first emitted and the series ended with the eruption of phonolitic lavas. The average peralkalinity index in these rocks is typically about 1.0 and, therefore, peralkaline rocks coexist with non-peralkaline ones. However, a maximum in peralkalinity is found in the ignimbritic rocks of the lower part of the series. In spite of the evident acid peralkaline tendencies of these rocks, it does not seem appropriate to classify them as pantellerites or comendites. Nor are they consistent with the genetic processes proposed for rocks of similar composition and oceanic environment.The crystallization of the feldspars controls the variation trends among the different magmas but the fractionation alone does not sufficiently explain the genesis of successive fluids. Various factors seem to point to the important role which a gas-transfer process causing a geochemical stratification inside the magmatic chamber may have played.The occurrence of peralkaline silicics at Gran Canaria, which is located for away from the active Mid-Atlantic ridge, is not related to transitional basalts. These rocks are a deviation from the main undersaturated alkalic trend which characterizes the volcanism of the Canary Islands, their genesis being related to the realization of favourable local volcanic conditions.  相似文献   

An Origin for the Linear Magnetic Anomalies on Mars through Accretion of Terranes: Implications for Dynamo Timing     

Alberto G. FairénJavier Ruiz  Francisco Anguita 《Icarus》2002,160(1):220-223

The proposed existence of magnetic lineations in the Terra Cimmeria and Terra Sirenum regions of Mars was initially explained by Earth-like sea-floor spreading. Here we argue instead that these lineations could have been formed at a convergent plate margin through collision and accretion of terranes. A similar process produced banded magnetic anomalies, similar in geometry and even in size to those in Earth's North American Cordillera. Because only sparse and generally weak anomalies have been detected in the martian northern lowlands, which could constitute an analog to the terrestrial oceanic crust, it is possible that the magnetic field stopped its activity while crustal recycling was still active in Mars.  相似文献   

Opening pupils' eyes to the skies     

Francisco Diego 《Astronomy& Geophysics》2006,47(5):5.18-5.20

Francisco Diego describes a successful outreach scheme that takes schoolchildren into an observatory and shows them what astronomy is all about.  相似文献   

Diffuse Emission of CO2 from Showa-Shinzan, Hokkaido, Japan: A Sign of Volcanic Dome Degassing   总被引：1，自引：0，他引：1  

Pedro A. Hernández  Kenji Notsu  Hiromu Okada  Toshiya Mori  Masanori Sato  Francisco Barahona  Nemesio M. Pérez 《Pure and Applied Geophysics》2006,163(4):869-881

Two soil CO₂ efflux surveys were carried out in September 1999 and June 2002 to study the spatial distribution of diffuse CO₂ degassing and estimate the total CO₂ output from Showa-Shinzan volcanic dome, Japan. Seventy-six and 81 measurements of CO₂ efflux were performed in 1999 and 2002, respectively, covering most of Showa-Shinzan volcano. Soil CO₂ efflux data showed a wide range of values up to 552 g m^-2 d^-1. Carbon isotope signatures of the soil CO₂ ranged from -0.9‰ to -30.9‰, suggesting a mixing between different carbon reservoirs. Most of the study area showed CO₂ efflux background values during the 1999 and 2002 surveys (B = 8.2 and 4.4 g m^-2 d^-1, respectively). The spatial distribution of CO₂ efflux anomalies for both surveys showed a good correlation with the soil temperature, indicating a similar origin for the extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of Showa-Shinzan. The total diffuse CO₂ output of Showa-Shinzan was estimated to be about 14.0–15.6 t d^-1 of CO₂ for an area of 0.53 km².  相似文献   

Development and behaviour of a radar-based operational tool for hailstorms identification     

Ismael San Ambrosio  Francisco Martín  Fermín Elizaga   《Atmospheric Research》2007,83(2-4):306-314

Hailstorms are a common meteorological phenomenon in Spain which causes substantial economic damage especially in spring and summer. During 2000 and 2001, a radar-based application for convective monitoring was developed at STAP (Forecasting and Analysis Techniques Department); in order to improve this nowcasting tool, it is needed to include an advanced procedure to estimate the presence of hail as a complementary module in the operational application. A preliminary study, carried out during 2001, showed that the Waldvogel technique, VIL (vertical integrated liquid) density and the hail detection algorithm (HDA) are the methodologies which proved more accurate in our latitudes.Throughout the spring and summer of 2001, all available information about hail events (time, place and hail size) and about storms without hail was used for tuning an experimental module to detect severe and non-severe hailstorms, taking into account the selected algorithms. During 2002, further information about storms was gathered in order to assess the behaviour of the developed hail module. Afterwards, a new module calibration was carried out with the information of the complete storms data set of 2001 and 2002. With this new calibration, the hail module became an operational tool during the spring and summer of 2003. Currently, the verification of the operational module using the data from the storms in 2003 is being elaborated. The aim of this work is to put forward the calibration procedure carried out, the verification results of 2002, and the performance of the hail estimate module in selected cases during 2003 in Spain.  相似文献   

Crustal attenuation in the Southern Andean retroarc (38°–39°30′ S) determined from tectonic and gravimetric studies: The Lonco-Luán asthenospheric anomaly     

Andrs Folguera  Antonio Introcaso  Mario Gimnez  Francisco Ruiz  Patricia Martinez  Cynthia Tunstall  Ezequiel García Morabito  Víctor A. Ramos 《Tectonophysics》2007,439(1-4):129-147

The western retroarc of the Southern Andes between 38° and 40° S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4–3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Expected crustal thickness at these latitudes is around 38 km, whereas in this part of the retroarc the thickness is less than 32 km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath the South American plate, which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 Ma. Gravimetric studies show that the upper plate did not react homogeneously to slab steepening, but ancient sutures and lithospheric discontinuities deeply buried under Mesozoic to Cenozoic sequences in the retroarc were locally reactivated. These processes resulted in an asthenospheric anomaly that correlates at the surface with the area of Pliocene to Quaternary doming, widespread extension and three radial troughs. Two of the troughs have accommodated substantial amounts of extension, but the third was probably aborted at an early stage. Moreover, the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly, and their age distribution, may indicate minor migration of the asthenospheric anomaly between 4 and 2 Ma through the western South American plate.  相似文献   

Structural framework and Mesozoic–Cenozoic evolution of Ponta Grossa Arch, Paraná Basin, southern Brazil     

Michael Strugale  Sidnei Pires Rostirolla  Fernando Mancini  Carlos Vieira Portela Filho  Francisco Jos Fonseca Ferreira  Rafael Corrêa de Freitas 《Journal of South American Earth Sciences》2007,24(2-4):203-227

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The Byers Basin: Jurassic-Cretaceous tectonic and depositional evolution of the forearc deposits of the South Shetland Islands and its implications for the northern Antarctic Peninsula     

Joaquin Bastias  Mauricio Calderón  Lea Israel  Francisco Hervé  Richard Spikings  Robert Pankhurst 《International Geology Review》2020,62(11):1467-1484

ABSTRACT

This paper addresses the Jurassic–Cretaceous stratigraphic evolution of fore-arc deposits exposed along the west coast of the northern Antarctic Peninsula. In the South Shetland Islands, Upper Jurassic deep-marine sediments are uncomformably overlain by a Lower Cretaceous volcaniclastic sequence that crops out on Livingston, Snow and Low islands. U-Pb zircon ages are presented for the upper Anchorage Formation (153.1 ± 1.7 Ma) and the Cape Wallace granodiorite of Low Island (137.1 ± 1.7 Ma) as well as ⁴⁰Ar/³⁹Ar ages of 136–139 Ma for Low Island andesites. Data are also presented for a U-Pb age of 109.0 ± 1.4 Ma for the upper volcanic succession of Snow Island. In combination with published stratigraphy, these data provide a refined chrono- and litho-stratigraphic framework for the deposits herein referred to as the Byers Basin. Tentative correlation is explored with previously described deposits on Adelaide and Alexander islands, which could suggest further continuation of the Byers Basin towards the south. We also discuss possible correlation of the Byers Basin with the Larsen Basin, a sequence that shows the evolution of foreland to back-arc deposits more or less contemporaneously with the fore-arc to intra-arc evolution of the Byers Basin.  相似文献   

Sequence stratigraphy of Holocene incised-valley fills and coastal evolution in the Gulf of Cádiz (southern Spain)     

Dabrio  Cristino J.  Zazo  Cari  Lario  Javier  Goy  José Luis  Sierro  Francisco J.  Borja  Francisco  González  José Ángel  Flores  José Abel 《Geologie en Mijnbouw》1998,77(3-4):263-281

This first sedimentary interpretation of two incised-valley fills in the Gulf of Cádiz (southern Spain), which accumulated during the last fourth-order eustatic cycle in response to fluvial incision, changes of sea level, and correlative deposition, relates the filling of the estuarine basins and their barriers with four regional progradation phases, H₁ to H₄. The cases studied are the wave-dominated Guadalete, and the mixed, tide and wave-dominated Odiel-Tinto estuaries. The sequence boundary is a type-1 surface produced during the lowstand of the Last Glacial period ca. 18 000 ¹⁴C yr BP. No fluvial lowstand deposits were found in the area. Due to rapid transgression the valley fills consist of transgressive and highstand sediments. The maximum landward advance of the estuarine barriers occurred ca. 6500–6000 ¹⁴C yr BP during the maximum of the Flandrian transgression, but there is no evidence of sea level rising appreciably above the present. A large part of the estuaries was filled during H₁ (ca. 6500–4400 ¹⁴C yr BP) but ravinement by shifting tidal inlets destroyed most of the coeval barriers. During the H₂ phase (ca. 4200–2550 ¹⁴C yr BP) sedimentation was favoured by arid conditions and concentrated in the axial estuarine zones and the barriers. Between H₂ and H₃ prevailing winds changed from W to WSW, increasing spit growth to the east and south-east. Progradation of bay-head deltas and flood-plains during H₃ (ca. 2300–800 ¹⁴C yr BP) and H₄ (500 yr ago to the present) further reduced the accommodation space in the largely-filled valleys, and sediment by-passed the estuaries and accumulated in the estuarine barriers as fast-growing spits. Arid conditions and increasing human activity have caused rapid coastal modifications.  相似文献