Single-station estimates of the seismic moment of the 1960 Chilean and 1964 Alaskan earthquakes,using the mantle magnitudeM m

Measurements are taken of the mantle magnitudeM _m , developed and introduced in previous papers, in the case of the 1960 Chilean and 1964 Alaskan earthquakes, by far the largest events ever recorded instrumentally. We show that theM _m algorithm recovers the seismic moment of these gigantic earthquakes with an accuracy (typically 0.2 to 0.3 units of magnitude, or a factor of 1.5 to 2 on the seismic moment) comparable to that achieved on modern, digital, datasets. In particular, this study proves that the mantle magnitudeM _m does not saturate for large events, as do standard magnitude scales, but rather keeps growing with seismic moment, even for the very largest earthquakes. We further prove that the algorithm can be applied in unfavorable experimental conditions, such as instruments with poor response at mantle periods, seismograms clipped due to limited recording dynamics, or even on microbarograph records of air coupled Rayleigh waves.In addition, we show that it is feasible to use acoustic-gravity air waves generated by those very largest earthquakes, to obtain an estimate of the seismic moment of the event along the general philosophy of the magnitude concept: a single-station measurement ignoring the details of the earthquake's focal mechanism and exact depth.     

Louvain-la-Neuve,Belgium, from campus to new town

Summary Louvain-la-Neuve, the sole Belgian New Town in three centuries, is located about thirty kilometers southwards of Brussels. In its first stage it had been established for welcoming most of the faculties of the Catholic University of Louvain (C. U. L.), which transferred from the original location in Louvain. The estate acquired by the C. U. L. mainly covers an agricultural area of 900 hectares, partly divided into 338 hectares for the future urbanized perimeter, 180 hectares for a public forest, and 163 hectares for a scientific park, designed for private research and development activities in connection with academic laboratories.The first part of the city center is almost completed and is located in the dale of the Malaise, on a substructure with underground parking and a railway station. Four neighbourhood units have been planned on the top of the slopes; the first two are already nearly finished and a third is under way. The principle of segregation of automobile and pedestrian traffic and its advanced architectural style constitute the main features.The active population of Louvain-la-Neuve now reaches about 12,000 (two-thirds are the students of the C. U. L.), and the residential population numbers more than 6,000 inhabitants (three-quarters are students and their families). The age structure is very young, due to the high proportion of students.Commuting to Louvain-la-Neuve is facilitated by excellent road and public transportation connections. As time goes by, it is anticipated that commuting will diminish. Moreover, a phenomenon of external commuting is developing. The attractive sphere and environment, the pedestrian areas and the emphyteotic system are the key features of the future residential development for persons neither professionally linked to the C. U. L. nor to the New Town.When the student transference is completed in 1979, the stage of real diversification of activities and functions will begin. About 20,000 inhabitants are scheduled for location by 1985 and a maximum of 50,000 by the end of the century. At that time, Louvain-la-Neuve together with its neighbours, Wavre and Ottignies, will form an urban tripole on a regional level, thereby strengthening the urban framework of the Walloon Brabant.     

Réflexions sur l'orogénèse quaternaire

Sans résumé     

Morphologie de la Méditerranée Occidentale

Résumé Partant de la grandiose conception d'Edouard Suess, la géologie de la Méditerranée a été divisée en quatre étages méditerranéens.Si le premier représente le début de la création d'une mer transgressive, le deuxième représente l'extension maximum de cette mer au delà de la chaîne alpine, puis il est suivi par une regression très générale. Au quatrième méditerranéen ou Pliocène, la mer pénètre dans toutes les vallées, dépressions du continent, réalisant la forme actuelle de cette mer où, depuis le Plaisancien se déposent les mêmes « argiles bleues » extraordinairement uniformes. Ces dépôts sont toujours très épais.Les unités morphologiques de la Méditerranée actuelle sont à peu près les mêmes que celles que les océanographes des Etats-Unis ont reconnu dans l'Atlantique: plaine littorale, plateau continental, pente continentale, plaine abyssale. Les sea-mounts ont même été reconnus en Tyrrhénienne et en Méditerranée Orientale. Les modifications du fond de la mer sont presque toujours dues au jeu des failles, soit d'effondrement comme en Tyrrhénienne, soit au contraire, de surrection, qui amènent à émerger d'anciens fonds de la mer.Les modifications corrélatives du fond de la mer, par abaissement et surtout par disjonction de la surface des continents, ont comme conséquences une regression depuis le Crétacé, entrecoupée de transgressions accompagnées d'épanchements de nature basaltique sur le fond de la mer. Ces mouvements se font de part et d'autre du pied de la Pente continentale qui est presque linéaire.A mon sens, les transformations de la Méditerranée se sont faites beaucoup plus autour des failles que par des plissements.

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Since the grand conception ofEdouard Suess, the geology of the Mediterranean has been divided into four Mediterranean stages.If the first stage represents the beginning of the creation of a transgressive sea, the second represents the maximum extension of this sea beyond the Alpine range, and is then followed by a general regression. At the fourth stage, Mediterranean or Pliocene, the sea imades all valleys, depressions of the adjoining continent, realizing the present form of this sea, where, since the Plaisancian, the same blue clays form thick deposits of extraordinarily uniform character.The morphologic units of the present Mediterranean are about the same as the cones that have been found in the Atlantic by the oceanographers of the United States: coastal plain, continental shelf, continental slope, abyssal plain. Even sea-mounts have been found in the Tyrrhenean sea and in the Eastern Mediterranean. The modifications of the bottom of the sea are mostly due to tectonics, either by lowering as in the Tyrrhenean sea, or, by rising, causing emergences.The correlative modifications of the sea-bottom, by subsidence and mostly by disjunction of the surface of the continents consequently display a regression since Cretaceous times, intersected by transgressions accompanied by submarin extrusions of a basaltic nature. Such movements occur at the foot of the (almost linear) continental slope.In my opinion, the transformations of the Mediterranean have occurred much more by faulting than by folding.

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Zusammenfassung Nach der grandiosen Konzeption von E.Suess ist die Geologie des Mittelmeeres in vier mediterrane Phasen gegliedert worden.Die erste Phase stellt den Beginn eines transgressiven Meeres dar, die zweite bezeichnet die maximale Ausdehnung dieses Meeres jenseits der Alpen, darauf folgt eine allgemeine Regression. Während der vierten Phase, dem Pliozän, dringt das Meer in alle Täler und Depressionen des Kontinents ein, wobei die heutige Form des Mittelmeeres entsteht, und mit dem Plaisancien kommt es zur Ablagerung der blauen Tone, die außerordentlich einheitlich und stets sehr mächtig sind. Die morphologischen Einheiten des heutigen Mittelmeeres sind etwa dieselben, wie sie die Ozeanographen der USA im Atlantik vorgefunden haben: Litoralebene, Kontinentalplateau, Kontinentalabhang, Tiefsee-Ebene. Die Seeberge (sea-mounts) wurden wiedererkannt im Tyrrhenischen Meer und im östlichen Mittelmeer. Die Veränderungen des Meeresgrundes sind fast immer auf die Wirkung von Verwerfungen zurückzuführen, wobei Senkung, wie im Tyrrhenischen Meer, stattfand oder aber Hebung zur Emersion des alten Meeresbodens führte. Die wechselseitigen Veränderungen des Meeresbodens durch Senkung und besonders durch Trennung der Kontinentoberflächen haben seit der Kreide eine Regression zur Folge, die von Transgressionen mit Basaltergüssen auf dem Meeresboden unterbrochen wurde. Diese Bewegungen fanden auf beiden Seiten am Fuße des Kontinentalabhanges statt, der fast linear ist.Nach meiner Meinung wurden die Umwandlungen des Mittelmeeres mehr durch Verwerfungen als durch Faltungen hervorgerufen.

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Essai sur Le déroulement du paroxysme alpin dans les Alpes Franco-Italiennes

In the French-Italian alpes three folding phases can be recognized; the first one was hardly known up to now.

1. 1.
   During the Lower Eocene; in some places starting already with the end of the Upper Cretaceous.     

Ilot de chaleur a Quebec: Cas d'ete

This paper studies the urban heat island in Quebec City and its suburbs on one summer night. The region under study covers an area of 20 km by 20 km which streches from lake Saint-Charles on the north to Levis on the south and from the western suburb of Cap-Rouge to Beauport on the east. The total population of the region is about 400 000.On August 22, 1979 from 22:00 to 23:30 EDT, 109 measurements of wet- and dry-bulb temperatures were taken at preselected points. On that day, a large high pressure system gave clear skies to central Quebec while Quebec City Airport recorded a maximum temperature of 23 °C. The average wind measured at Duberger meteorological tower between 6 and 121 m above ground was 1.8 m s^-1 at 22:00 EDT and 0.9 m s^-1 at 23:30 EDT. Additional data were obtained from three thermographs installed at strategic points and five regular climatological stations, which were used to estimate cooling rates.During the period of measurement, the cooling rate averaged over the eight reference points was about 0.7 °C h^-1. However, the maximum cooling rate, which occured earlier, ranged from 2.2 °C h^-1 at Duberger to 4.4 °C h^-1 at Courville-de-Poissy. No relation seems to exist, in our case, between the maximum cooling rate and the heat island spatial structure. Comparison of these results with the ones given by Oke et al. (1972) shows that the eight stations behaved more like rural stations than urban ones.The temperature gradient measured between the center of old Quebec City and the suburbs averaged 6 °C while it was 9 °C for the coldest spot. Clo units were used to characterize the microclimates prevailing on the region for that night; 1 clo would be sufficient for comfort downtown while 1.5 clo is needed in the coldest spot for a slowly walking person. Large open areas like parks or the Laval University campus had a definite effect on temperature.The humidity was calculated for each point using standard psychrometric tables; no significant difference could be found over the area expect at points near or above the St. Laurent river where the average dew point was 1.5 °C higher.Each point was classified into 6 categories according to its predominant land-use as reported by the observers. A multiple regression between temperature on the one hand and altitude and land-use on the other hand was tried; it showed that temperature was significantly correlated with both. Such an equation could be used by town-planners to locate temperature gradients in future urban development over the area; land uses could be planned to enhance or reduce these gradients.This study confirms the idea that urban climate is a mosaic of interacting micro-climates. More measurements, including possibly airborne infra-red thermal imagery, will be taken during winter in order to assess the winter urban climate of Quebec City.     

Coupes Sismiques des Structures Superficielles dans les Petites Antilles—II: Martinique

Résumé En 1977, deux profils sismiques ont été réalisés en Martinique, un dans la région volcanique de la Montagne Pelée, l'autre dans la partie est de l'île. Le premier couvrait des distances de 3 à 23 km et le second de 2 à 50 km.Les structures superficielles du volcan sont interprétées par un modèle à trois couches. Sur une couche déjà connue, à 6,1 km/s nous trouvons, avec une épaisseur de 0,4 à 2,6 km, une vitesse de 4,3 km/s. En surface et jusqu'à une profondeur de 0,8 à 1,4 km la vitesse est d'environ 2,7 à 2,9 km/s.Dans la partie est de la Martinique, il existe une vitesse élevée-6,5 km/s—à partir d'une profondeur faible, de l'ordre de 3 km.

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In 1977, two seismic profiles were carried out in Martinique, one in the area of Montagne Pelée volcano, and the second in the eastern part of the island. The length of the first profile ranges from 3 to 23 km and the second from 2 to 50 km. The interpretation shows that the superficial structures of the volcano may be characterized by a three layer model: in the first layer the compressional velocity is about 2.7 to 2.9 km/s, the thickness varying from 0.8 to 1.4 km. The second layer has a velocity of 4.3 km/s and the thickness goes from 0.4 to 2.6 km. The deeper layer known at Leeward West Indies has a 6.1 km/s velocity.The second profile shows that the eastern part of Martinique is marked by a high velocity of 6.5 km/s, found at a depth of 3 km.

     

Huge landslide blocks in the growth of piton de la fournaise, La réunion, and Kilauea volcano, Hawaii

Piton de la Fournaise, on the island of La Réunion, and Kilauea volcano, on the island of Hawaii, are active, basaltic shield volcanoes growing on the flanks of much larger shield volcanoes in intraplate tectonic environments. Past studies have shown that the average rate of magma production and the chemistry of lavas are quite similar for both volcanoes. We propose a structural similarity — specifically, that periodic displacement of parts of the shields as huge landslide blocks is a common mode of growth. In each instance, the unstable blocks are within a rift-zone-bounded, unbuttressed flank of the shield. At Kilauea, well-documented landslide blocks form relatively surficial parts of a much larger rift-zone-bounded block; scarps of the Hilina fault system mark the headwalls of the active blocks. At Fournaise, Hilina-like slump blocks are also present along the unbuttressed east coast of the volcano. In addition, however, the existence of a set of faults nested around the present caldera and northeast and southeast rift zones suggests that past chapters in the history of Fournaise included the slumping of entire rift-zone-bounded blocks themselves. These nested faults become younger to the east southeast and apparently record one of the effects of a migration of the focus of volcanism in that direction. Repeated dilation along the present set of northeast and southeast rift zones, most recently exemplified by an eruption in 1977, suggests that the past history of rift-zone-bounded slumping will eventually be repeated. The record provided by the succession of slump blocks on Fournaise is apparently at a relatively detailed part of a migration of magmatic focus that has advanced at least 30 km to the east-southeast from neighboring Piton des Neiges, an extinct Pliocene to Pleistocene volcano.     

Cordierite-garnet-H2O equilibrium: A geological thermometer,barometer and water fugacity indicator

The high-grade assemblage Cd-Ga-Si-Qz can be thermodynamically modelled from available calorimetric data on the metastable reaction: (I) $$3 MgCd \rightleftarrows 2 Py + 4 Si + 5 Qz$$ naturalK _D ^Fe-Mg between garnet and cordierite and experimental results on cordierite hydration. In the system SiO₂-Al₂O₃-MgO-H₂O, reaction (I) becomes (II) $$3 MgCd \cdot nH_2 O \rightleftarrows 2 Py + 4 Si + 5 Qz + 3 nH_2 O$$ . However, hydrous cordierite is neither a hydrate nor a solid solution between water and anhydrous cordierite and when nH₂O (number of moles of H₂O in Cd) is plotted against \(P_{H_2 O} \) , the resulting isotherms are similar to adsorption isotherms characteristic of zeolitic minerals. Reaction (II) can thus be considered as a combination of reaction (I) with a physical equilibrium of the type nH₂O (in Cd)?nH₂O (in vapor phase). Starting from a point on equilibrium (I), introduction of H₂O into anhydrous Mg-cordierite lowers the chemical potential of MgCd and hence stabilizes this mineral to higher pressure relative to the right-hand assemblage in reaction (I). The pressure increment of stabilization,ΔP, above the pressure limit of anhydrous cordierite stability at constantT, has been calculated using the standard thermodynamics of adsorption isotherms. Cordierite is regarded as a mixture of Mg₂Al₄Si₅O₁₈ and H₂O. The activity of H₂O in the cordierite is evaluated relative to an hypothetical standard state extrapolated from infinite H₂O dilution, by using measured hydration data. The activity of Mg₂Al₄Si₅O₁₈ in the cordierite is then obtained by integration of the Gibbs-Duhem equation, and the pressure stabilization increment,ΔP, computed by means of the relation: $$\Delta V_s \Delta P \cong - RT\ln a_{MgCd}^{MgCd \cdot nH2O} \left( {\Delta V indepentdent of P and T} \right)$$ . Thus, one may contour theP-T plane in isopleths of nH₂O=constant within the area of Mg-cordierite stability allowed by the hydration data for \(P_{H_2 O} = P_{total} \) . The present model indicates greater stabilization of cordierite by H₂O than the model of Newton and Wood (1979) and the calculated curve for metastable breakdown of hydrous MgCd is consistent with experimental data on cordierite breakdown at \(P_{H_2 O} = P_{total} \) . Mg/(Mg+Fe) isopleths have been derived for cordierites of varying nH₂O in the SiO₂-Al₂O₃-MgO-FeO-H₂O system using the additional assumptions that (Fe, Mg) cordierite and (Fe, Mg) garnet behave as ideal solutions, and that typical values of the distribution coefficient of Fe and Mg between coexisting garnet and cordierite observed in natural parageneses can be applied to the calculations. The calculated stable breakdown curve of Fe-cordierite under conditions of \(P_{H_2 O} = P_{total} \) to almandine, sillimanite, quartz and vapor has a positive slope (dP/dT) apparently in contrast to the experimental negative slope. This may be explained by hydration kinetics, which could have allowed systematic breakdown of cordierites of metastable hydration states in the experiments. The bivariant Cd-Ga fields calibrated from the present model are, potentially, good petrogenetic indicators, as, given the iron-magnesium ratio of garnet and cordierite and the hydration number of cordierite, the temperature, pressure and water fugacity are uniquely determined. As this geothermobarometer is in part based on the water content of cordierite, it can be used only if there is some assurance that the actual hydration is inherited from high-grade metamorphic conditions. Such conditions could be realised if the slope of unloading-cooling retrograde metamorphism is more or less parallel to a cordierite isohydron.