Assessment of project THRUST: Past,present, future

Project THRUST (Tsunami Hazards Reduction Utilizing Systems Technology) was a demonstration of satellite technology, used with existing tsunami warning methods, to create a low cost, reliable, local tsunami warning system. The major objectives were successfully realized at the end of the demonstration phase in September 1987. In June 1988, the Chilean Government held a workshop to assess the value of THRUST to national interests. Two recommendations came forth from the workshop: (1) the technology was sufficiently reliable and cost-effective to begin the development of an operational prototype and (2) the prototype would be used as the Chilean Tsunami Warning System. As of August 1989, the equipment was in operational use. In September 1989, major improvements were made in the satellite operations that reduced the response time from 88 to 17 sec and enlarged the broadcast area by 50%. The implications of the recent improvements in satellite technology are discussed for application to reductions in disaster impacts.     

Gravity-induced stresses in stratified rock masses

Summary This paper presents closed-form solutions for the stress field induced by gravity in anisotropic and stratified rock masses. These rocks are assumed to be laterally restrained. The rock mass consists of finite mechanical units, each unit being modeled as a homogeneous, transversely isotropic or isotropic linearly elastic material. The following results are found. The nature of the gravity induced stress field in a stratified rock mass depends on the elastic properties of each rock unit and how these properties vary with depth. It is thermodynamically admissible for the induced horizontal stress component in a given stratified rock mass to exceed the vertical stress component in certain units and to be smaller in other units; this is not possible for the classical unstratified isotropic solution. Examples are presented to explore the nature of the gravity induced stress field in stratified rock masses. It is found that a decrease in rock mass anisotropy and a stiffening of rock masses with depth can generate stress distributions comparable to empirical hyperbolic distributions previously proposed in the literature.     

Age et croissance de la truite lacustre (Salmo trutta lacustris L.) du Léman

The age and growth of adult Lake Geneva trout (Salmo trutta lacustris L.) caught from 1964 to 1974 for mark-and-recapture experiments was studied by scale analysis. The median lengths of 3 years and older fish were fitted to Von Bertalanffy growth curves. Their growth rates are higher than those of the fish younger than 3 years. It is conculded that this increase of growth rate concides with beginning of life in the lake, after the downstream migration of the juvenile trout which probably takes place in the second and third summer. No general increase of growth rates between cohorts could be detected from the beginning to the end of the period studied, in spite of a serious increase of eutrophication of Lake Geneva during the same time.      

Mesozoic evolution of the upper mantle beneath the eastern Pyrenees: evidence from xenoliths in Triassic and Cretaceous alkaline volcanics of the eastern Corbières (France)

Upper mantle material can be sampled from two distinctive suites in the North Pyrenean Zone (NPZ) of the Pyrenees. These occur either as ultramafic tectonic slices in the central and western part of the NPZ, or as discrete xenoliths in alkaline magmas in its eastern part, know as the Corbières. In the eastern part of the PNZ, two ultramafic xenolith suites have been found. The first suite is enclosed within Triassic basalts and the second suite is enclosed within Cretaceous monchiquites. Both suites essentially comprise spinel peridotites showing varying degrees of depletion, but each clearly distinguishable by texture and mineral chemistry.

The Triassic suite of ultramafic xenoliths is characterized by coarse texture and homogeneous composition of mineral constituents. This records equilibrium temperature of around 950 ° C before inclusion in the host basalt. They represent fragments of an upper mantle type normally occurring beneath continental rift systems.

The Cretaceous suite of ultramafic xenoliths display porphyroclastic textures, which grade locally to ultramylonites. The pyroxene porphyroclasts are compositionally zoned, titanian pargasite is ubiquitous, and equilibrium temperatures of around 750–800 ° C are indicated. They appear to be similar to peridotites occurring in ultramafic tectonic massifs in the NPZ, and with a common texture, mineralogy and thermal history. This indicates therefore that shear deformation and alkaline magmatism, experienced during the Middle Cretaceous, affected the upper mantle along the entire length of the NPZ. This can then be related to the regional transcurrent movements that were produced by sinistral strike-slip of Iberia with respect to the rest of Europe.     

A random process for earthquake simulation

Some existing models for the simulation of earthquake acceleration show the difficulties in determining the involved parameters and in describing frequency content. A non-stationary modulated random process obtained as the product of a time envelope function and a stationary random function is used to simulate earthquake acceleration. The parameters and the distribution of frequencies of the simulation process are obtainable from past earthquake records. This simple and realistic model is suggested for use as the input process in aseismic design of structures.     

Calc-alkaline and shoshonitic lavas from five Andean volcanoes (between latitudes 21° 45′ and 24°30′S) and the distribution of the Plio-Quaternary volcanism of the south-central and southern Andes

The Plio-Quaternary volcanic rocks of the south-central Andes (southward from latitude 18°S) contain two associations: calc-alkaline and shoshonitic which coincide with seismic belts as geographically distinct zones aligned parallel to the oceanic trench. There is a continuous gradation from calc-alkaline to shoshonitic associations. The shoshonitic association appears to the north of latitude 26°S; southwards, the calc-alkaline association directly abuts against the continental (Argentinian) alkaline association.Thirty-one lavas from the Plio-Quaternary calc-alkaline Socompa, Lascar, Sairecabur and Tocorpuri and shoshonitic Sierra de Lipez volcanoes were studied. The lavas are porphyric with abundant glass. The distribution and the nature of the phenocrysts vary according to the chemistry of the calc-alkaline lavas. Petrographic evidence for crystal fractionation has been observed. Occasional phenocrysts of alkali feldspars occur in the shoshonitic lavas. The K₂O and SiO₂ contents increase from calc-alkaline to shoshonitic lavas with distance away from the oceanic trench. In lavas from Socompa, Lascar, Sairecabur and Tocorpuri calc-alkaline volcanoes, K₂O, Li and Rb increase and K/Rb and Sr decrease with increasing SiO₂; Ba increases with decreasing Sr, probably as a result of plagioclase fractionation. In lavas from Sierra de Lípez shoshonitic volcano, SiO₂ is high, K₂O is high and rather constant and Li, Rb, Ba and Sr increase with increasing SiO₂. Bolivian shoshonitic lavas appear to be genetically related to the calc-alkaline suite.The calc-alkaline lavas may be derived by crystal fractionation from a parental magma of andesitic nature that originated in or above the subjacent Benioff zone.     

The thermodynamic properties of reciprocal solid solutions

A multisite solid solution of the type (A, B) (X, Y) has the four possible components AX, AY, BX, BY. Taking the standard state to be the pure phase at the pressure and temperature of interest, the mixing of these components is shown not to be ideal unless the condition: $$\Delta G^0 = (\mu _{AX}^0 + \mu _{BY}^0 - \mu _{AY}^0 - \mu _{BX}^0 = 0$$ applies. Even for the case in which mixing on each of the individual sublattices is ideal, ΔG ⁰ contributes terms of the following form to the activity coefficients of the constituent components: $$RT\ln \gamma _{AX} = - X_{B_1 } X_{Y_2 } \Delta G^0$$ (X _Ji refers to the atomic fraction of J on sublattice i). The above equation, which assumes complete disorder on (A, B) sites and on (X, Y) sites is extended to the general n-component case. Methods of combining the “cross-site” or reciprocal terms with non-ideal terms for each of the individual sites are also described. The reciprocal terms appear to be significant in many geologically important solid solutions, and clinopyroxene, garnet and spinel solid solutions are all used as examples. Finally, it is shown that the assumption of complete disorder only applies under the condition: $$\Delta G^0 \ll zn_1 RT$$ where z is the number of nearest-neighbour (X, Y) sites around A and n ₁ is the number of (A, B) sites in the formula unit. If ΔG ⁰ is relatively large, then substantial short range oder must occur and the activity coefficient is given by (ignoring individual site terms): $$\gamma _{AX} = \left( {\frac{{1 - X'_{Y_2 } }}{{1 - X_{Y_2 } }}} \right)^{zn_1 }$$ where X′_Y2 is the equilibrium atomic fraction of Y atoms surrounding A atoms in the structure. The ordered model may be developed for multicomponent solutions and individual site interactions added, but numerical methods are needed to solve the simultaneous equations involved.     

Petrology,volume and age relations of alkaline and saturated peralkaline volcanics from Terceira,Azores

Four volcanoes form Terceira, one of the islands of the Azores group; three contain both basaltic and peralkaline and one only peralkaline rocks. A recently active basaltic fissure zone trends NW-SE across the island.The rocks fall into the alkaline olivine basalt suite although some young basalts are of transitional affinity. The geochemistry shows two general basaltic series: 1) undersaturated, found in lavas of the oldest volcano and in some recent fissure zone basalts and hawaiites; 2) saturated, found in the younger basaltic lavas.Since the emergence of Terceira there has been a contemporaneity of basalt and salic peralkaline lavas. The younger rocks show a bimodal composition distribution, the most voluminous compositions being alkali olivine basalt and comendite with negligible volume in the benmoreite-trachyte range. Two processes appear viable for the derivation of voluminous oversaturated peralkaline rocks: 1) partial melting of upper mantle material giving small magma batches of contrasting composition or 2) fractionation from a transitional basaltic parental magma.Now at Department of Geology, Victoria University of Wellington, New Zealand.     

Premier Apport de la Geochimie des Isotopes du Soufre à la Comprehension de la Genese des Mineralisations Pyriteuses de la Province de Huelva (Espagne) par

Sans résuméCe travail a pu être réalisé grâce à une subvention de la D.G.R.S.T.