Institut De Physique Du Globe Research Articles

Supernovae: Little Bear's mass loss rate

Supernovae: Little Bear's mass loss rate

Foreign correspondents

Three distinguished mineral physicists—Ian Jackson of the Research School of Earth Sciences at the Australian National University, Canberra; Jean‐Paul Poirier of the Institut de Physique du Globe at the Universite of Paris VI; and Takehiko Yagi of Tohoku University, Sendai, Japan—have been appointed foreign correspondents to the AGU Committee on Mineral Physics. Their reports to the AGU Committee and to Mineral Physics News will strengthen the international ties that are essential in the interdisciplinary study of mineral physics

Eruption at Le Piton de la Fournaise volcano on 3 February 1981

Piton de la Fournaise in the island of La Reunion, Indian Ocean, is a young (0.35-Myr old) basaltic shield volcano built on the flank of the extinct Piton des Neiges volcano. It is one of the most active volcanoes in the world (magma output rate of 0.32 m3 s−1)1,2 and has been under continuous surveillance by the Volcanological Observatory of the Institut de Physique du Globe de Paris since August 1980. The first detailed observations on the volcano reveal a remarkably low level of background seismicity. The 3 February 1981 eruption was preceded by a deep event of volcanic origin at depths of 10–15 km on 2 January; 20 days of quiescence followed this event, until the onset of shallow seismicity close to the eruptive centres on 22 January. The eruption began after 13 days of sustained shallow seismicity and occurred in three phases over 92 days and produced about 10 × 106 m3 of lava.

In situ determination of the hydrothermal properties of a deep fractured medium by a single-well technique

The recovery of energy from deep hot rock formations with low permeability gives rise to many scientific and technological problems. This paper describes a simple method of in situ analysis of a slightly fissured medium, developed by the Centre d'Informatique Géologique of the Paris School of Mines, during experiments carried out at the site of Mayet de Montagne (Allier, France) between November 1978 and March 1980. These experiments were funded by the Commission of the European Communities and the Institut National d'Astronomie et de Géophysique, and carried out jointly with the Institut de Physique du Globe, Paris. They had a two-fold purpose: 1. (1) Better understanding of the physical phenomena governing the heat exchange between the slightly fissured medium and the injected fluids. 2. (2) Determination in situ of the parameters which control this exchange. This proposed “single-well” method might be suitable as a preliminary test in order to evaluate the life span of a hot dry rock geothermal doublet.

Geodetic results in Afar: The rifting episode of November 1978 in the Asal-Ghoubbet rift

A seismo-tectonic and volcanic crisis occurred in November 1978 in the Asal-Ghoubbet rift, first subaerial section of the accreting plate boundary between the African and Arabian plates (Allard et al., 1979; Abdallah et al., 1979; Le Dain et al., 1980). The activity was located in the center of a geodetic network set up in the winter 1972–1973 by the Institut Géographique National in collaboration with the Institut de Physique du Globe de Paris. Simultaneously, a precise levelling line of about 100 km was established across the area (I.G.N., 1973). The resurveying of both the geodetic network and the levelling line was carried out after the crisis, between November 1978 and March 1979. Extensions up to 2.4 m and vertical displacements up to 0.7 m were measured. Operating techniques and results of the resurveying are described in Kasser et al. (1979) and Ruegg et al. (1979). Figure 1 shows the horizontal displacements (relating to point B and to the direction BT) and figure 2 shows the vertical displacements relating to the two external points. Tarantola et al. (1979, 1980) have shown that these results can be geodynamically interpreted by a mechanism of sudden breaking and elastic rebound after an elastic stretching of the crust due to the relative drift of the plates. The breaking is triggered by magmatic fracturing of the crust, with dykes injection from a magmatic chamber which has fed the basaltic fissurai eruption. The horizontal and vertical displacements outside the broken zone of the Inner Floor are predicted by a numerical model based on this interpretation which fit very well the experimental data.

Report from IUGG Assembly: “Mayaud” symposium on use of geophysical indices

This symposium was held by the International Association of Geomagnetism and Aeronomy (IAGA), at the XVII IUGG General Assembly in Canberra, Australia, 1979, to honor P. N. Mayaud of the Institut de Physique du Globe, Paris. Mayaud was recognized for his long years of service toward the development and improvement of geomagnetic indices. Mayaud has now retired and will be sorely missed by his many colleagues around the world. However, he is leaving a legacy to his coworkers in the form of Deviation, Meaning, and Use of Geomagnetic Indices (Geophysical Monograph Series, vol 22), to be published by AGU in 1980.

Investigation of crustal structure by the analysis of reverberation periodicities

abstract The analysis of reverberation periodicities is shown to be a promising method to study local crustal structure. It is demonstrated with the help of numerical models, that for an average crust; a data length of only 8 to 12 sec is sufficient to derive a crustal model in contrast to about 40 sec or more needed in the Phinney's spectral ratio matching technique. Examples from numerical models of one- and two-layer crusts are presented. Analysis of five intermediate and deep focus earthquakes, recorded on magnetic tape at the Echery (ECH) observatory of the Institut de Physique du Globe of Strasbourg, shows that while the spectral ratios indicate little overall coherence, the periodicity corresponding to the total crustal thickness is evident in all cases. The possibility of deriving a detailed crustal model is also discussed with the help of results from one of the above events.

Etude séismique des explosions d’Haslach

In April 1948 the «Institut de Physique du Globe, Strasbourg » has been carrying out a program of seismic work on important explosions in the Black Forest. Seismic waves were recorded by 21 stations mainly along the profile between Strasbourg and the Alps across the Elack Forest and the «Schwâbische Alb ». The authors describe the explosive charges (nature, position, etc.), the instruments and techniques utilized, the regional geology and the complete readings of the records. Evidence for the existence of four layers is shown : gneiss-granit : h1 = 2.4 km ; v1 = 5,63 km/s deep-granit : h2 = 17.7 km ; v2 = 5,97 km/s gabbro-basalt : h.3 = 10. 1 km ; v3 = 6,54 km/s peridotit : v4 = 8,15 km/s The basaltic layer is very well defined : the P. impulses are very clearly shown, also the reflections on the upper part of the intermediate layer. It appears that this layer formerly supplied the lava of the old volcanoes in southern Germany ; in this area the Mohorovici discontinuity is at a depth of about 30 kilometers. These results and the different wave-velocities obtained are discussed and compared with the previous ones. The studies of natural earthquakes in southern Germany differ partly from our results : the problem of «calculated depth of focus » requires further research work. A large bibliography concludes the paper.

Geophysical Observations in France

THE third volume of the “Annales” of the Institut de Physique du Globe de l'Universite de Paris and of the Bureau Central de Magnetisme Terrestre, the two institutions directed by Prof. Maurain, has been issued recently (Paris: Les Presses Universitaires de France, 1925). The volume is devoted mainly to observations made during the year 1923. The principal geophysical observatory in France is at Val-Joyeux, 24 kilometres west of Paris. For this observatory hourly values of the magnetic elements are published. Systematic magnetic observations have been re-established recently at Nantes on the lower Loire, and the results of the first complete year's work are now given. It appears that, in spite of the disturbance due to electric trams, which come within 450 metres of the Observatory at Nantes, there is satisfactory agreement between the two stations, which are in nearly the same latitude. For the year 1923 the range of the mean diurnal variation of declination was 6-46′ at Val-Joyeux and 6.33′ at Nantes; the corresponding figures for horizontal force were 167 and 167.

Report on the dissolution meeting of the International Seismological Association, Strasbourg, April 24–25, 1922

The delegates met at the Institute de Physique du Globe, Strasbourg, April 24–25, 1922. The following allied nations were represented by delegates: Belgium, Brazil, Canada, France, Great Britain, Japan, Norway, Portugal, Spain, Switzerland, United States.Dr. Hecker (Germany), former director of the Central Bureau of the Association, and Professor de Kovesligethy (Hungary), former secretary were present. Several other states of Central Europe were represented by proxy.