Recent large earthquakes from a geophysical perspective

In recent times our society has been disturbed by the effect of various earthquakes (Haiti, Chile, New Zealand, and Japan). These are not new phenomena, the Earth has been and will be subjected to their action, but large earthquakes are not frequent or occur elsewhere. There are regions of the Earth more likely than others to be affected by them. In addition, an adequately society can be prepared to mitigate the risk. Knowing the hazard of each area is essential in order to reduce the effect of earthquakes, which implies the thorough study of their features and of areas in which they occur. This article reviews the recent major earthquakes from a geophysical perspective and analyzes the characteristics and the specific geological context in which they occur. For this analysis, the records of earthquakes obtained at LEGEF stations, which can be found on our website (http://sismic2.iec.cat) have been used

Métodos de inversión numérica para la interpretación de perfiles sísmicos

Tesis Univ. Complutense de Madrid, 1980.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEProQuestpu

Métodos de inversión numérica para la interpretación de perfiles sísmicos

Tesis Univ. Complutense de Madrid, 1980.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEProQuestpu

Los aludes. Actuaciones para la reducción de su peligrosidad.

Snow avalanches are a natural hazard whose negative consequences have multiplied in recent times owing to demographic expansion and increased infrastructures in mountain areas. Therefore, the minimisation of the negative consequences of avalanches is essential. The steps to be taken are as follows: make a snow avalanche cartography, know the avalanche return period, obtain some knowledge of the triggering mechanism in relation to the snow properties and determine the values of the physical parameters of the avalanche evolution in order to minimise the impact. The complexity of this natural phenomenon calls for a multidisciplinary collaboration on a global scale in order to pool our efforts and lines of research. A number of strategies to improve the understanding of formation, evolution and effect of avalanches are presented

Fundamentos de geofísica. A. Udías i J. Mezcua. Alianza Universidad textos, 2a ed. revisada (Barcelona, 1998), AUT 167, 476 pig.

El llibre, tal com els seus autors ho indiquen, recull una llarga experiència en la docència de Geofísica a les facultats de Física de Barcelona i Madrid. Tracta del que es denomina geofísica de la Terra sòlida o geofísica interna i és dels poquíssims llibres sobre aquesta matèria en llengua castellana, i l'únic escrit originàriament en aquesta llengua. Desafortunadament, no existeixen textos sobre aquesta matèria en català

Coneixement de la litosfera a partir de perfils sísmics

Una de les línies d'investigació en 1'àmbit de les ciències de la Terra és l'estudi de la litosfera, és a dir, aproximadament els 100-200 primers quilòmetres de la Terra. La litosfera inclou l'escorça terrestre (30-40 km) i una part del mantell superior. El coneixement de la litosfera és molt important per a la humanitat, ja que hi estan lligats els fenòmens relatius a l'activitat de la Terra, que alhora l'afecten, com ara els terratrèmols i els volcans. A més, el seu coneixement està directament relacionat amb el seu aprofitament (camps geotèrmics. energia fòssil...). El coneixement que avui dia tenim deis paràmetres físics de la litosfera a partir de mesures directes és molt escàs. Existeixen diversos sondatges arreu del món que no superen els 3 o 4 km de fondària. Hi ha un sondatge profund (13 km) a la península de Kola i també n'està previst un altre de profund (anomenat KTB) a Bavària (Alemanya), que actualment no ha superat els 5 km. La informació obtinguda d'aquests sondatges és útil, però ni la cobertura ni la fondària són suficients per treure conclusions generals sobre les característiques de la litosfera. En realitat. el coneixement de la litosfera s'obté de manera indirecta a partir d'observacions a la superfície terrestre

Estudi de la sismicitat de Catalunya

Els primers resultats d'un treball que caldrà continua

Snow avalanche energy estimation from seismic signal analysis

A method to determine the dissipated seismic energy into the ground by a down going avalanche is presented. Evaluation of the seismic energy is useful for avalanche size classification, model validation, and for characterization and better understanding of the avalanche evolution as it propagates downhill along the changing slope. The method was applied to two different type avalanches that were released artificially on 2004/02/28 and 2005/04/15 at Ryggfonn (Norway) avalanche experimental site, operated by the Norwegian Geotechnical Institute (NGI). The analysed seismic data were recorded by the University of Barcelona seismic instruments consisting of two three-component wide-range seismometers located respectively, in the middle and on the side of the avalanche path. The energy determination requires a priori seismic characterization of the site and the knowledge of the avalanche front speed. In this paper a seismic characterization (surface wave phase velocity and amplitude attenuation factor) of the Ryggfonn site is presented. This characterization will serve for subsequent studies. We attribute the main source of seismic signals for the studied events to basal friction and ploughing occurring at the avalanche front and related to the changing slope in the propagation path, which causes high seismic energy dissipation. A comparative study of the evolution of the dissipated seismic energy with the energy generated by a simple sliding block model of constant mass was performed. The observed differences highlight the importance of ploughing and basal friction and the specific characteristics of the avalanches, such as their length and type. The difference between the calculated total dissipated seismic energy for the two similar size avalanches reflects their different flow type. As expected, the dry/mixed event dissipates a smaller amount of energy (not, vert, similar 1.2 MJ) than the dry/dense event (not, vert, similar 2.8 MJ)