Inconsistent patterns of historical seismicity and earthquake-triggered landsliding in southeastern Sicily: an alarm bell?

In southeastern Sicily, the distribution pattern of earthquake-triggered landslides is inconsistent with historically known seismic activity. In particular, historical seismicity has been stronger in the eastern sector, while earthquake-triggered landsliding is much more developed in the western sector, and this contrasts with expectations. This paper describes the patterns of seismicity and landsliding, and tackles the problem of whether greater landsliding in the western sector may be due (a) to seismicity of the eastern sector or (b) to a high-magnitude, low-recurrence seismicity generated in the western sector itself. It is statistically shown that lithostructural characteristics of rock masses and geometry of hillslopes cannot justify, either singly or jointly, greater landsliding in the western sector if triggering earthquakes are generated in the eastern sector. As a consequence, it is possible that landsliding of the western sector is due to earthquakes generated locally, but having higher magnitude and longer recurrence intervals than historically observed.     

Coseismic rotation changes from the 2004 Sumatra earthquake: the effects of Earth's compressibility versus earthquake induced topography

Polar motion is modelled for the large 2004 Sumatra earthquake via dislocation theory for an incompressible elastic earth model, where inertia perturbations are due to earthquake-triggered topography of density–contrast interfaces, and for a compressible model, where inertia perturbation due to compression-dilatation of Earth's material is included; density and elastic parameters are based on a multilayered reference Earth. Both models are based on analytical Green's functions, propagated from the centre to the Earth's surface. Preliminary and updated seismological solutions are considered in elucidating the effects of improving earthquake parameters on polar motion. The large Sumatra thrust earthquake was particularly efficient in driving polar motion since it was responsible for large material displacements occurring orthogonally to the strike of the earthquake and to the Earth's surface, as imaged by GRACE gravity anomalies over the earthquake area. The effects of earthquake-induced topography are four times larger than the effects of Earth's compressibility, for l = 2 geopotential components. For varying compressional Earth properties and seismic solution, modelled polar motion ranges from 8.6 to 9.4 cm in amplitude and between 117° and 130° east longitude in direction. The close relationship between polar motion direction, earthquake longitude and thrust nature of the event, are established in terms of basic physical concepts.     

Domains of spit evolution in the Goro area, Po Delta, Italy

Goro lagoon was formed during the 19th century in the southern part of the Po Delta. Its origin is related to the growth of a spit system, which progressively occluded the southernmost interdistributary bay from the sea. The development of the spits is due to the morphological prominence of the Po Delta which causes a divergent littoral drift, enhanced by wave refraction over the delta front. During the last century the spit was abandoned, destroyed, and re-constructed several times because of the development of newer spits seawards. Using historical maps and aerial photographs, three different periods are recognised, featuring distinctive spit growth styles: parallel, fan-shaped and branched. The different domains of spit evolution are related to several factors, mainly to the mutual influence of sediment discharge, sand mining along the Po river, wave action over the delta front, human-induced subsidence and direct human interventions along the spits and for flood-control.     

Effects of turbulence development in solar surges

Several authors have claimed for correlations between surges (dark features) and various kinds of solar emissions (radio, microwave, X-ray). In this paper we propose a model to explain such correlations, in particular presenting the properties of the instabilities resulting from the coupling between material flow, connected to the appearance of a surge, and magnetic field topology. As a consequence of such instability a turbulent energy cascade to small characteristic lengths grows up. Depending of the relevant parameters of the surge (dark feature), different regimes can be found, producing different levels of electrons acceleration and mass motion deceleration. We try then to correlate the different developments of the instability with the behavior observed in type I and type III radio bursts related to surges.Proceedings of the Second CERSA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

A kinematic evolutionary model for the Penninic sector of the central Ligurian Alps

The nappe pile presently cropping out in the central sector of the Ligurian Alps, is represented by some principal groups of tectonic units. Starting from the foreland, the outer and lower, weakly metamorphic (up to 0.3 GPa) Briançonnais units support the high-pressure (up to 1.3 GPa) ensemble of inner Briançonnais nappes, in turn overridden by the Prepiedmont units, sourced from the European continental margin. Prepiedmont units form two superposed groups. The lower is composed only of a pre-Namurian basement (Alpine metamorphism up to 0.6 GPa); and the upper is mainly composed of a slightly metamorphic (greenschist facies) post-Namurian cover. At the top lie the high-pressure metamorphosed (up to 0.8 GPa in the sector here considered) ophiolitic units. The group of the non-metamorphic Helminthoid Flysch nappes (original stratigraphic cover of the ophiolitic units) has travelled the greatest distance and is presently mainly set onto the outer part of the chain. Only events up to the stacking of the nappe pile are discussed, disregarding late-stage deformation. As the examined sector is located at a considerable distance from the collisional zone, late processes did not change the overall order of superposition formerly acquired. The model proposes the development of two major, subhorizontal detachment surfaces. The first, shallower one confines at the base a very thin-skinned set of nappes, nearly totally made up of Prepiedmont sedimentary covers that are bounded at their top by the Helminthoid Flysch units. Both these groups underwent a mainly horizontal outwards transport. In contrast, the underlying Prepiedmont crust and the adjoining Briançonnais inner sector (separated by the second, deeper major detachment surface) were progressively dragged into the subduction zone under the ophiolitic units and duplexes were generated. Exhumation of the metamorphic units occurred along the subduction channel, as did stacking of the nappe pile.     

Genèse des magmas du volcanisme plio-quaternaire des Apennins

Zusammenfassung Nach einer kurzen Übersicht des Vulkanismus in der Gegend des heutigen Appeninns im oberen Jura (basischer Vulkanismus im Tiefseegraben) und im Eozän (kalkalkaliner Vulkanismus während der Tektogenese) wird der pliozäne und quartäre, durch anatektische Magmen gespeiste Vulkanismus des unter Dehnung stehenden Orogens ausführlicher behandelt. Dieser Vulkanismus äußerte sich auf der thyrrhenischen Seite des Appennins zwischen dem Arno und dem Tiber im Zusammenhang mit dem Hochdringen mehrerer kleiner Granitstöcke, deren ältester 7 Millionen Jahre alt ist, während das Alter des jüngsten nur 3 1/2 Millionen Jahre beträgt. Der Beweis wird erbracht, daß es sich um anatektische Magmen handelt, und die mutmaßliche Ursache der unvollständigen Anatexis und der Differentiation der durch diese entstandenen Magmen besprochen. Eine Hypothese zur Erklärung der Entstehung von kalireichen, femischen Differentiaten wird vorgeschlagen. Danach wird, unter Berücksichtigung der quantitativen Beziehungen der einzelnen Magmatypen, ein Gesamtbild des aktiven Vulkanismus entworfen, der gesättigte und untersättigte kalireiche Magmen längs einer 300 km langen Zone vom nördlichen Latium bis zum Vesuv förderte. Es folgt eine Diskussion über das Problem des Stammagmas dieses Vulkanismus und der dazu vorgeschlagenen Hypothesen. Geologische, magmatologische und geochemische Tatsachen machen es wahrscheinlich, daß die mediterranen Magmatypen durch eine komplexe Differentation eines tief liegenden, anatektischen Magmas entstanden sind. Zum Schluß wird der Versuch unternommen, die Entstehung und Evolution der Magmen der periappenninischen Vulkane der Insel Capraia (Toskanischer Archipel), der Pontinischen Inseln und des einzigen, östlich vom Appennin liegenden Vulkans des Monte Vulture zu erklären.

---

After a short survey of the volcanic activity around the chain of the Apennines during the upper Jurassic (basic and submarine ophiolitic volcanism) and during the Eocene (calc-alkaline volcanism of the early tectonic stages), a more detailed picture of plio-quaternary volcanism derived from anatectic magma during the distensive stage of orogenesis is given. This volcanic activity has taken place on the tyrrhenian side of the Apennines between the Arno and Tiber rivers and is connected with the uplift of some little granitic stocks, ranging between 7 m. y. and 3,5 m. y. Some arguments on the anatectic origin of magma, on its differentiation and on the possible causes of the incomplete anatexis are reported. An hypothesis is proposed to explain the genesis of some highly mafic and alkaline differenciates. A general picture is also given of the volcanic activity derived from saturated or undersaturated alkaline magma, along a zone of 300 km from northern Latium to Vesuvius. The parental magma origin of this volcanism and the several hypotheses regarding this problem are discussed. The geological, magmatological and geochemical data make probable the hypothesis that the mediterranean volcanic rocks were produced by a complex mechanism of differentiation of a deep-seated anatectic magma. Finally, some hypotheses on the origin and the evolution of magmas of the periapenninian volcanoes are given (Capraia and Pontine islands, and M. Vulture, the latter being the only recent volcano localized on the eastern side of the Apennines).

---

Résumé Après une vue d'ensemble de l'activité volcanique dans la région de la chaîne des Apennins à la fin du Jurassique (volcanisme basique sousmarin) et au cours de l'Eocène (volcanisme alcali-calcique [calco-alcalin] pendant la tectogénèse), le volcanisme Pliocène et Quaternaire, nourri par des magmas anatectiques pendant le stade distensive de l'orogénèse est traité. Ce volcanisme du côté tyrrhénien de l'Apennin, entre l'Arno et le Tibre, est lié à la mise en place de plusieurs petits stocks granitiques, dont le plus vieux a 7 millions d'années, le plus récent n'en a que 3 1/2 millions.Il est prouvé que ce sont des magmas anatectiques; la raison pour l'anatexie régionale, la différenciation des magmas est traité. Une hypothèse qui pourrait expliquer l'origine des roches fémiques et potassiques est donné.Une vue plus générale du volcanisme actif, produisant des magmas potassiques saturés et sous-saturés le long d'une zone de 300 km du nord du Latium au Vsesuve est donné, bien regardant les relations quantitatives entre les types différents de magma. Le problème du magma primaire de cette activité volcanique et plusieurs hypothèses sont discutés. Des raisons géologiques, magmatologiques et géochimiques font supposer que les types de magma méditerrané sont dérivés par différenciation d'un magma d'anatexie resté en profondeur. Reste enfin à expliquer l'origine et l'évolution des magmas trouvés dans les volcans périapennins de l'île Capraia (Archipel Toscan), des îles Pontiennes et du Monte Vulture, seul volcan du côté oriental de la chaîne des Apennins.

---

, . ; 7 3 1/2 . . , . , . , , .

     

Temperature in volcanism

Direct or indirect temperature measurements of magmas erupted by volcanoes are still very scarse. All available thermal data have been measured in lava lakes and on volcanoes with limited explosive activity, i. e. the data refer to basic products. Explosive activity, which prevails for 80 % of the active volcanoes, prevents any measurement. The thermal data show that all basic magmas, whatever their origin and tectonic position may be, reach the surface within the same temperature interval. This seems to be related to the fact that all basic magmas are in equilibrium with some solid phases.The great improvement of physico-chemical knowledge of equilibrium conditions of artificial melts allows a more precise utilization of geologic thermometers. The plagioclase geothermometer can be used to evaluate the spreading rate of plates in oceanic rift zones.The heat of magmas offers an energy source of great importance for the future. The highest probability of finding high temperatures at relatively shallow depths for use as geothermal energy is obviously in the proximity of active volcanoes. Programs to extract energy directly from such shallow-seated magma sources have been taken into consideration in the Kamchatka peninsula/SU and on Hawaii/USA.

---

Zusammenfassung Direkte und indirekte Temperaturmessungen von geschmolzenen Förderprodukten der Vulkane sind sehr spärlich. Solche Messungen sind bislang nur bei Eruptionen basischer Magmen ausgeführt worden, da diese von Natur aus wenig oder gar nicht explosiv sind. Hinzu kommen Messungen der Temperatur in den seltenen Lava-Seen. Alle diese Messungen zeigen, daß die magmatischen Produkte verschiedener Herkunft die Oberfläche immer im gleichen Temperatur-Intervall erreichen. Diese Tatsache dürfte darin ihren Grund haben, daß alle basischen Magmen im Gleichgewicht mit festen Phasen sehr ähnlicher Zusammensetzung stehen. Die indirekten Bestimmungen der Temperatur mittels geologischer Thermometer, wie z. B. die Zusammensetzung der erstausgeschiedenen Plagioklase in Basalten, die längs der sich öffnenden mittelozeanischen Rücken zu Tage kommen, können nützliche Hinweise geben auf die Geschwindigkeit des Auseinanderdriftens der Platten.Die Anwesenheit von bedeutenden Mengen hochtemperierter Magmen, die einen Teil ihrer Wärme an die Oberfläche abgeben, hat neuerdings zu Überlegungen geführt, wie daraus geothermische Energie nutzbar zu machen ist. Solche geothermisch nutzbaren Gebiete gibt es z. B. in Kamtchatka/UdSSR und auf Hawaii/USA.

---

Riassunto Le misure dirette o indirette di temperatura dei materiali fusi emessi dai vulcani attivi sono molto scarse e si riferiscono solamente a eruzioni di magmi basici poco o punto esplosive o ai rari laghi di lava incandescente. Tutte le misure esistenti indicano comunque che prodotti magmatici di origine diversa arrivano in superficie nello stesso intervallo di temperature. Ciò può essere in relazione al fatto che tutti i magmi basici sono in equilibrio con fasi solide di composizione molto simile. Le misure indirette di temperatura eseguite con geotermometri, ad esempio la composizione del plagioclasio di cristallizzazione iniziale nei basalti delle zone di spreading oceanico, possono fornire utili indicazioni sulla velocità di allontanamento delle placche.La presenza di quantità importanti di magmi a temperatura elevata che dissipano parte del loro calore vicino alla superficie ha fatto recentemente prendere in considerazione la possibilità di sfruttamento di energia geotermica nelle aree di vulcani attivi sia negli USA che nell'URSS.

---

. , .. . . , . , , , . , .: , , . , , . (CCCP) (CACIII).

     

Evolution of Eolian arc volcanism (Southern Tyrrhenian Sea)

The Eolian arc is located at the boundary between the converging African and European plates. Its volcanism is characterized by a marked evolution in a restricted time (less than 1 my). A progressive transition is observed from typical calc-alkaline series toward shoshonitic rocks produced by past and present activity (Vulcano and Stromboli). By comparison with circum-Pacific island arcs, the evolution of Eolian volcanism can be related to a rapid deepening of the Benioff zone. The occurrence of shoshonitic rocks and the continental nature of the crust on both sides of the plate boundary suggest that the Eolian arc is in a senile stage of evolution. Petrology and Sr isotopic data indicate a probable mantle source for Eolian volcanism.