Unites structurales de la marge continentale sous-marine de Cannes a Menton d'apres la sismique refraction

Offshore seismic refraction profiles permitted us to characterize the extent of the geological formations which prolong the principal units of the Provence and Alpes Maritimes southwards and to establish their respective relationships. The concept of a “Var graben” is confirmed and defined. A magma chamber, probably in relation with the volcanic deposits of the Cap d'Ail, has been disclosed and coincides with the positive magnetic anomaly observed in this area.     

Étude des spectres du signal sismique initial lors d'un tir nucléaire souterrain. Determination du coefficient d'atténuation dans le granite

Résumé A l'aide de formules empiriques, établies à partir des valeurs des amplitudes spectrales obtenues au sein d'un massif à différentes distances du point zéro et pour des tirs de puissances échelonnées, on calcule les spectres des signaux sur la surface de la sphère inélastique-élastique où l'on admet que débute le signal sismique proprement dit. Ces spectres sont d'autant plus plats que l'énergie du tir est faible. La comparaison des spectres obtenus à des distances variables permet de montrer que le coefficient d'atténuation exponentielle en fonction de la fréquence est proportionnel à celle-ci, ce qui confirme l'hypothèse de la constance du facteur de qualitéQ.Summary From the spectral amplitudes obtained at several distances from underground explosions for several values of the emitted energy, we calculate the same spectrum on the sphere where the seismic signal is supposed to begin. This spectrum becomes more flat if the energy becomes smaller. A comparison between the spectra which are obtained at several distances, shows that the exponential attenuation coefficient is proportional to the frequency. This confirms the hypothesis of a constance of the quality factorQ.     

Sur un modele explicatif de l'arc de Gibraltar

Many authors have explained the Gibraltar arc in various manners. It is our purpose to set up an explanation which takes into account the recent geological discoveries about the Geology of this region, and the concept of Plate Tectonics. Stratigraphic, metamorphic and structural arguments support the fundamental opposition between internal and external zones in the Betic-Rif mountain system. Internal zones, clearly showing an arcuate structure, were built before Miocene. External zones, on the contrary, were folded mainly during Middle Miocene. Both zones have been involved in important shortening (with strike-slip faulting) just before Messinian (late Miocene). Taking into account the later deformations, we can assume that the internal zones constituted, at the beginning of the Miocene, the sub-plate of Alboran, which separated, eastwards from the Azores transform-fault, the European and African plates. According to this model, we can suppose the Alboran sub-plate to be fixed, whereas the European and African plates move eastwards. So, tectonic structures oblique to the direction of drift, like folds and thrusts along a transcurrent-fault, appear along the north-western and south-western margins of the Alboran sub-plate; along its western margin, N-S structures form, thrusting towards the west. Our geometrical model is able to account for peculiar and unexplained structures of this region. Because of its simplicity, we are conscious of the limits of our explanation, but it seems to us to be a valuable working hypothesis, which needs further geophysical and geological tests.     

Evolution de l'état sanitaire de la baie d'Auvernier (lac de Neuchâtel) de 1962 à 1973

The evolution of the trophic state of a part of the Lake of Neuchâtel was investigated by means of a study of 4 parameters (temperature, dissolved oxygen, total phosphorus and nitrates) in the waters of the Auvernier Bay (fig. 1). Each year is composed of a stratification period (June to November) and a circulation period (December to May) (fig. 2). Notwithstanding the heavy consumption of oxygen in the metalimnion during the stratification period, the waters are sufficiently abundant in dissolved oxygen (fig. 3). As a matter of fact, over the 12-year period studied, no decrease in the oxygen content was observed at any depth (fig. 4). On the other hand, the quantities of nutrients were enriched in nitrates (30%) and phosphorus (230%) (fig. 5–8). The Auvernier Bay may be thought to have evolved from an oligotrophic state in 1963 to an eutrophic state in 1972 if we consider only these latter two criteria.     

Exact solution of the source problem for a finite threedimensional source

Summary In this note the surface displacement for an elastic half-space due to a finite cylindrical source has been calculated in exact terms. The source consists of outward body forces acting on the surface of the right circular cylinder, one end of which is parallel to the free surface of the half-space.     

Eutrophisation et faune benthique de trois lacs de montagne

Zoobenthic communities were used to indicate the trophic state of three mountain lakes of western Switzerland. In these lakes, the macrobenthos was constituted mainly by oligochaetes and chironomid larvae;Tubifex tubifex was the most abundant worm species. In Lakes Lioson and Hongrin, the abundance of zoobenthos did not change or increased slightly with depth andStylodrilus heringianus was present. In Lake Chavonnes, zoobenthos decreased strongly with depth and it consisted mainly ofTubifex tubifex. These data, compared with those from other oligotrophic lakes, indicated that Lake Chavonnes was eutrophic whereas Lakes Lioson and Hongrin were oligotrophic. However, Lake Hongrin—an artificial lake made in 1968—constituted a special case. Its water comes in part from mountain rivers and in part from Lake Geneva. Consequently, some benthic species of Lake Geneva have colonized Lake Hongrin and its water is warmer than in a typical mountain lake.      

Examen de quelques formules pour la predetermination de l'epaisseur du glacier a l'occasion de sondages recents

Summary Thirty years ago, when no easy and efficient process of sounding could reveal them the true depth of a glacier,C. Somigliana tried to help the glaciologist with a formula giving them the maximal thickness of any transverse section. Requisites were: breadth, maximal velocity, slope and coefficient of internal friction to be known. Commanding condition: no gliding of the ice on the glacier-bed. Numerous recent soundings of Swiss ice-streams did afford the opportunity of verifying the pertinency of the formula. Therefore the writer selected sixteen of the most reliable soundings and reckoned the values of the coefficient of viscosity . The results have been deceptive: if however the mean value of differs not much from 10¹⁴ CGS usually accepted (afterLagally), the divergencies are very great, extending from less than the half to almost the double (The same is been shown for the recent formulae ofHaefeli andKoechlin). Therefore no secure number can be derived for the required depth. The condition of no gliding is mostly not realized and the are therefore lessened. If however the real value of for the ice can ever be ascertained it will be possible to reckon the velocity of the up to now unmeasured gliding of the ice on the bed.     

Alimentation et facteurs de mortalité des larves de corégones (Coregonus sp.). Exemple de deux lacs de niveaux trophiques différents: Les lacs de Sarnen et de Hallwil (Suisse Centrale)

Whitefish larvae (Coregonus sp.) were caught at regular intervals in 1986 and 1987 in oligotrophic Lake Sarnen, and in 1987 in eutrophic Lake Hallwil.The food spectra of the larvae in each lake were directly related to the available prey organisms.The causes for the important decrease of the larval catches in Lake Sarnen observed in 1987 are examined.There was no significant difference in the abundance and size distribution of the principal zooplankton taxa between the 1986 and 1987 samples. The effects of a sudden cooling of the surface water layer on the survival of cold-bred whitefish larvae are discussed.     

各向同性膨胀点源模拟长白山火山区岩浆囊压力变形源

2002～2003年长白山火山区的水平运动缺乏中心对称性分布特征,本文采用同一深度沿三个互相垂直方向拉张的点源模式模拟了长白山火山区的岩浆囊压力变形源. 在介质参数为Vp＝6.700 km/s,Vs＝3.8700 km/s,ρ＝2900 kg/m3的均匀弹性半空间中, 联合利用2002～2003年长白山火山区的GPS观测数据和水准数据, 结合PSGRN/PSCMP代码和遗传算法反演长白山火山区的压力变形源特征. 反演结果表明,由三个垂直的不等量扩张方向确定的椭球状点源模型可以较好地模拟长白山火山区岩浆囊压力变形源. 岩浆囊深处9.2 km,在走向为34.4°,倾角为82.2°的断层面的法向方向体积扩张量最大,达到7000000 m3;在走向为302.8°,倾角为78.5°的断层面的法向方向体积扩张量次之,达到6598071 m3;在走向为337.7°,倾角为14.0°的断层面的法向方向体积扩张量最小,达到5220160 m3.     

Studies on seismic source

During the period of 1999~2002, the Chinese seismologists made a serious of developments in the study on seismic sources including observations, experiments and theory. In the field of observation, the methods of the accuracy location of earthquake sources, the inversion of seismic moment tensor and the mechanism of earthquake source are improved and developed. A lot of important earthquake events are studied by using these methods. The rupture processes of these events are inverted and investigated combined with the local stress fields and the tectonic moment by using the measurements of surface deformation. In the fields of experiments and theory, many developments are obtained in cause of seismic formation, condition of stress and tectonics, dynamics of earthquake rupture, rock fracture and nucleation of strong earthquakes.     

Studies on seismic source

During the period of 1999-2002, the Chinese seismologists made a serious of developments in the study on seis-mic sources including observations, experiments and theory. In the field of observation, the methods of the accu-racy location of earthquake sources, the inversion of seismic moment tensor and the mechanism of earthquake source are improved and developed. A lot of important earthquake events are studied by using these methods. The rupture processes of these events are inverted and investigated combined with the local stress fields and the tec-tonic moment by using the measurements of surface deformation. In the fields of experiments and theory, many developments are obtained in cause of seismic formation, condition of stress and tectonics, dynamics of earthquake rupture, rock fracture and nucleation of strong earthquakes.     

Ondes de surface

Résumé Le but de ce mémoire est de démontrer quelques nouvelles propriétés générales d'une classe de fonctions (les ondes de surface) très importante par son rôle en physique et en géophysique.On commence par la démontration d'un théoréme fondamental qui établit l'identité de l'ensemble des ondes de surface et de l'ensemble des fonctions pour lesquelles, à tout instantt ₀ et en tout pointA ₀ de leur domaine d'existence, on peut écrire une proportionnalité entre intervalles de temps (situés, en général asymétriquement, de part et d'autre det ₀) et rayons des domaines circulaires centrés enA ₀, telle que les moyennes temporelles et spatiales correspondantes soient égales. Ce théorème permet d'écrire, en termes finis, la solution des équations aux dérivées partielles de toute onde de surface.On applique ensuite les résultats généraux: 1° à la variation diurne de la pression lce qui permet de voir que ce phénomène peut être considéré comme une onde de surface et donne la loi fondamentale en cos³ ( latitude) pour l'amplitude de l'onde semidiurne progressive]; 2° aux ondes de variation de la pression synoptique. Pour ces ondes de variation on établit les relations qui existent entre leurs paramètres caractéristiques et on détermine finalement leur configuration théorique.

---

Summary The aim of this paper is to give the proof of some new general properties of a class of functions (the surface waves) which is very important in physics and geophysics.We first give the proof of a fundamental theorem establishing the identity of the set of all surface waves and the set of functions for which, at any momentt ₀ and at any pointA ₀ of their domain, there exists a proportionality between time intervals comprisingt ₀ (asymmetrically, in the general case) and the radius of the circular domains centered onA ₀, such that the corresponding temporal and spatial means are equal. This theorem allows to write in finite terms the solution of the partial differential equations of any surface wave.The general results are then applied: 1° to the diurnal pressure variation, showing that this phenomenon can be considered as a surface wave and giving the fundamental law cos³ ( latitude) for the amplitude of the progressive or travelling 12-hourly wave; 2° to the waves of the synoptic pressure variations. For these waves the relations between their characteristic parameters is first established and finally their theoretical spatial configuration or pattern is deduced.

---

---

Communication faite le 23 Avril 1957 à la Cinquième Assemblée de la «Società Italiana di Geofisica e Meteorologia» (Genova, 23–25 Avril 1957).