Analysis of sustained long-period activity at Etna Volcano, Italy

Following the installation of a broadband network on Mt. Etna, sustained Long-Period (LP) activity was recorded accompanying a period of total quiescence and the subsequent onset of the 2004–2005 effusive episode. From about 56000 events detected by an automatic classification procedure, we analyse a subset of about 3000 signals spanning the December 17th, 2003–September 25th, 2004, time interval. LP spectra are characterised by several, unevenly-spaced narrow peaks spanning the 0.5–10 Hz frequency band. These peaks are common to all the recording sites of the network, and different from those associated with tremor signals. Throughout the analysed time interval, LP spectra and waveforms maintain significant similarity, thus indicating the involvement of a non-destructive source process that we interpret in terms of the resonance of a fluid-filled buried cavity. Polarisation analysis indicates radiation from a non-isotropic source involving large amounts of shear. Concurrently with LP signals, recordings from the summit station also depict Very-Long-Period (VLP) pulses whose rectilinear motion points to a region located beneath the summit craters at depths ranging between 800 and 1100 m beneath the surface. Based on a refined repicking of similar waveforms, we obtain robust locations for a selected subset of the most energetic LP events from probabilistic inversion of travel-times calculated for a 3D heterogenous structure. LP sources cluster in a narrow volume located beneath the summit craters, and extending to a maximum depth of ≈ 800 m beneath the surface. No causal relationships are observed between LP, VLP and tremor activities and the onset of the 2004–2005 lava effusions, thus indicating that magmatic overpressure played a limited role in triggering this eruption. These data represent the very first observation of LP and VLP activity at Etna during non-eruptive periods, and open the way to the quantitative modelling of the geometry and dynamics of the shallow plumbing system.     

高空急流入口区次级环流在一次突发性强降水过程中的作用

通过对 1999年秋季一次突发性降水过程高空急流的分析 ,发现急流入口区南侧辐散 ,其低层辐合上升 ,当低层有印缅槽活动的时候 ,对流加强 ,印缅槽发展 ;急流入口区北侧辐合 ,其低层辐散下沉 ,有向南的非地转风     

山东南墅地区孔兹岩系变质矿物的成因及演化

南墅地区孔兹岩系的变质矿物具有多成因、多世代的特征 ,其经历三阶段五幕的变质作用 ,形成了以Sil+Gt +Cord +Bi +Kf +Pl+Q为代表的共生矿物组合。通过对主要变质矿物成因及演化特征的分析 ,结合温压计估算 ,确定该区孔兹岩系峰期变质作用温度为 70 0～ 75 0℃ ,压力为 0 .6～0 .7GPa ,变质程度达角闪麻粒岩相。确立 pTt轨迹具顺时针演化特点 ,反映一种陆 -陆碰撞造山带式构造演化模式。     

Improved dynamic correction method in seismic analysis of both classically and non‐classically damped structures

A step‐by‐step approximate procedure taking into consideration high‐frequency modes, usually neglected in the modal analysis of both classically and non‐classically damped structures, is presented. This procedure can be considered as an extension of traditional modal correction methods, like the mode‐acceleration method and the dynamic correction method, which are very effective for structural systems subjected to forcing functions described by analytical laws. The proposed procedure, herein called improved dynamic correction method, requires two steps. In the first step, the number of differential equations of motion are reduced and consequently solved by using the first few undamped mode‐shapes. In the second step, the errors due to modal truncation are reduced by correcting the dynamic response and solving a new set of differential equations, formally similar to the original differential equations of motion. The difference between the two groups of differential equations lies in the forcing vector, which is evaluated in such a way as to correct the effects of modal truncation on applied loads. Copyright © 2001 John Wiley & Sons, Ltd.     

Ein Pollendiagramm aus dem Untergrund des Zürichsees

Zusammenfassung Im Sommer 1952 wurden von Prof.Otto Jaag im Zürichsee cine Reihe von Tiefenbohrungen ausgeführt. Ein Bohrkern von 830 cm L?nge, der in 140 m Seetiefe entnommen worden war, wurde pollenanalytisch durchge-gearbeitet. Der See erreicht an dieser Stelle seine gr?sste Tiefe, und sein Boden ist auf einer Fl?che von 1000 m Breite und 7000 m L?nge ganz flach, was dafür Gew?hr bietet, dass die Sedimentation ungest?rt vor sich gehen konnte. Der Bohrkern bestand aus tonreichem Mergel oder unreiner Soekreide, mit einzelnen Einlagerungen von Sand (Abb. 2). Er reichte bis in die waldfreie Zeit des Sp?tglazials hinab. Die Ergebnisse der Pollenanalyse sind in den Abbildungen 2 und 3 zusammengestellt. In Abbildung 2, rechts aussen, wird versucht, die Ablagerung nach den Zeitstufen vonBlytt-Sernander undFranz Firbas zu gliedern. Dabei ergaben sich Schwierigkeiten, und es ist fraglich, ob die natürlichen Grenzen in unserm Diagramm mit der zeitlich festgelegten Periodeneinteilung der oben genannten Forscher immer in übereinstimmung gebracht werden k?nnen. Auch wenn die gleiche Waldfolge gefunden wird, so dürften die Waldzeiten im Alpenvorland teilweise wesentlich früher in Erscheinung getreten sein als weiter gegen Norden hin.

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Summary During the summer of 1952 several deep boring into the underground of the Zürich-see were carried out by Prof. Dr.O. Jaag. One boring core with a length of 830 cm obtained under 140 m lake water was carefully investigated by pollenanalysis. In the spot from where this core originated, the lake reaches its greatest depth and its bottom is entirely flat within an area of 1000 m to 7000 m, which guarantees that the sedimentary process could continue without disturbance. The boring core consisted of loamy marl or lake-lime (Seekreide) with very few sandy layers (Fig. 2). The eldest samples date from woodless late-glacial time. Results of pollenanalysis are summarized in Figures 2 and 3. In Figure 2 (right outside) it was tried to divide the deposit into time-periods according toBlytt-Sernander andF. Firbas. However there arose certain difficulties and it remains doubtful, whether the natural limits in our diagram agree in each case with the fixed periods of the above named authors. Even where the same sequence of forest-development is found it is likely that some of the same forestperiods were realized considerably earlier in the foreland of the Alps than in northernmore parts of Europe.

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Die vorliegende Studie bildet einen Bestandteil der von Prof. Dr.O. Jaag organisierten Sediment-Untersuchung im Zürichsee. Die Durchführung der Bohrungen, die im Jahre 1952 stattfanden, wurde erm?glicht dank grosszügiger finanzieller Unterstützung durch dieVolkart-Stiftung, Winterthur, durch dieKulturkommission der Gemeinde Zollikon ZH sowie durch dieBeh?rden der Stadt und des Kantons Zürich. Bisher wurde ver?ffentlicht:H. Züllig,Sedimente als Ausdruck des Zustandes eines Gew?ssers, Schweiz. Z. Hydrol.18 (1956).     

Un procedimento per l'aggiustamento delle grandi triangolazioni

Riassunto In una nota diA. Marussi è stato rilevato che se, dopo aver compensato una triangolazione con le sole condizioni intrinseche, si impongono ulteriori condizioni come la coincidenza di alcuni vertici in punti prefissati, è possible determinare con sufficiente precisione le coordinate dei rimanenti vertici attraverso corrispondenze analitiche che soddisfino le condizioni di contorno e col requisito di limitare gli errori lineari e angolari. — L'Autore della presente nota propone una nuova corrispondenza, cioè quella atta a rappresentare le deformazioni di una membrana o rete elastica sottoposta ad assumere una data configurazione; stabilisce le equazioni per la rete elastica piana e sferica; mette in evidenza come il principio fisico della minima energia e quello matematico dei minimi quadrati conducano alle medesime equazioni.

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Summary A. Marussi has pointed out that if, after having compensated a triangulation with the intrinsic conditions only, we impose further conditions as the coincidence of some vertex in prefixed points, we can determinate the coordinates of the other vertex: that happens through analytical connections fulling contour conditions and limiting linear and angular errors.The present Author proposes a new connection, which is apt to represent the deformations of an elastic network which is to get a given configuration. He fixes the equations for the spherical and plane networks; points out how the physical principle of the least energy and the mathematical one of the least squares may give the same equations.

     

Structural physical parameter identification based on evolutionary-simplex algorithm and structural dynamic response

Evolutionary computation based on the idea of biologic evolution is one type of global optimization algorithm that uses self-adaptation, self-organization and random searching to solve optimization problems. The evolutionary-simplex algorithm is introduced in this paper. It contains floating encoding which combines the evolutionary computation and the simplex algorithm to ovcrcomc the problems encountered in the genetic algorithm and evolutionary strategy methods.Numerical cxpcrimcnts arc performed using seven typical functions to verify the algorithm. An inverse analysis method to identify structural physical parameters based on incomplete dynamic responses obtained from the analysis in the time domain is prcscntcd by using the evolutionary-simplex algorithm. The modal evolutionary-simplex algorithm converted from the time domain to the modal domain is proposed to improve the inverse efficiency. Numerical calculations for a 50-DOF system show that whcn compared with other methods, the evolutionary-simplex algorithm offers advantages of high precision,cfficient searching ability, strong ability to resist noise, independence of initial value, and good adaptation to incomplete information conditions.     

Seismic study of the Mesozoic carbonate basement around Mt. Somma–Vesuvius, Italy

Fifteen seismic reflection lines from AGIP surveys, in and around the Campanian Plain and Mt. Somma–Vesuvius (south Italy) have been interpreted. The attention has been focused to the horizon pertinent to the top of the Mesozoic carbonate sequence and the Quaternary faults dissecting it. As a matter of fact, both are very important elements for understanding the origin of the volcanic activity in the area, that often in the past, has been the topic of debates not supported by reliable data. In the study area, referring to the depth of the carbonate basement, comparison between the result achieved by the seismic prospecting and previous gravity studies has been made. It shows coherence in some areas but large discrepancy within others. Near the town of S. Anastasia, the gravity and seismic depth estimates differ as much as 1000 m or more. Furthermore, the seismic data show that the source of the greatest volcanic eruption in the area (the so-called ‘Campanian Ignimbrite') is probably not located in the Acerra depression, as suggested by other authors. A main NE–SW fault directed toward Vesuvius, considered as playing a primary role on volcanogenetic processes and previously recognised only offshore by marine seismic survey, has been now identified also inland using this new seismic information. The results presented here strengthen the hypothesis that Mt. Vesuvius is located at the crossing point of two regional Quaternary sets of fault heading NW–SE and NE–SW.