Migration of seismic data

Prospecting for oil and gas resources poses the problem of determining the geological structure of the earth's crust from indirect measurements. Seismic migration is an acoustic image reconstruction technique based on the inversion of the scalar wave equation. Extensive computation is necessary before reliable information can be extracted from large sets of recorded data. In this paper a collection of industrial migration techniques, each giving rise to a data parallel algorithm, is outlined. Computer simulations on synthetic seismic data illustrate the problem and the approach.     

Diffraction of love waves by two staggered perfectly weak half-planes

Summary Love wave travelling in a layer of uniform thickness overlying a half-space is assumed to be incident on two parallel but staggered perfectly weak half-planes lying in the upper layer. The diffracted field is calculated using the modified Wiener-Hopf technique and contour integration method. The diffracted waves satisfy the dispersion relations appropriate to different regions formed by the perfectly weak half-planes. To the memory of M. H. Kazi     

Prediction of the ground motion in Italy: a preliminary attempt

Summary The strong-motion accelerograms written by moderate and strong earthquakes occurring in Central Italy in recent years have been used to estimate physical quantities characterizing the spectrum of motion in the band of engineering interest (0.1 Hz≲f≲20 Hz). The source, propagation and site response parameters obtained in these analyses have therefore been employed to check if theoretical models may be used to correctly predict the trend of the peak values of seismic excitationvs. earthquake size in the areas investigated. For the selected data set, representative of a seismotectonic environment generating earthquakes with prevalent normal faulting (up to a magnitudeM _l ∼7, at depths varying roughly from 5 to 15 km), the assumed spectral model allows successful statistical predictions showing that specific site response is the main factor responsible for the large fluctuations often observed in the data behaviour, at similar magnitudes and distances from focus.

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Riassunto Gli accelerogrammi registrati in occasione di terremoti da moderati a forti nell'Italia Centrale negli ultimi anni sono stati utilizzati per la stima delle grandezze fisiche che caratterizzano lo spettro del moto nella banda di interesse ingegneristico (0.1 Hz≲f≲20 Hz). La parametrizzazione ottenuta per descrivere, mediamente, i meccanismi della sorgente, della propagazione e degli effetti di sito è stata quindi usata per verificare se i modelli teorici possono essere utilmente usati per prevedere gli andamenti dei valori di picco del moto in funzione dell'entità del terremoto. Per i dati selezionati, rappresentativi di un ambiente sismotettonico in grado di generare terremoti con meccanismi prevalentemente distensivi (fino ad una magnitudoM _l ∼7, con profondità variabile all'incirca tra 5 e 15 km), il modello spettrale prescelto consente delle previsioni soddisfacenti da un punto di vista statistico, mostrando che la specifica risponsta dei siti è probabilmente il fattore che provoca le sensibili fluttuazioni spesso osservate per i valori di picco del moto, anche a parità di magnitudo e distanza dal fuoco.

     

Arguments in favour of a program of seismic detection of gravity wave bursts

Summary The possibility is shown of selecting gravity wave perturbations in earth crust block in the seismic-noise background due to far local sources. It is shown that the utilization of different space-time ?colourations? of gravity wave and noise perturbations makes it possible, in principle, to extract the signal in the background of noise of exceeding intensity.     

On a new general theory of earthquakes

Summary Some phenomena have been observed a very brief time before an intense earthquake: variations of the terrestrial magnetic and electric fields, rumble and also often animal nervousness. In order to give a sole explanation of all these phenomena, a general theory of the earthquake has been built, based on separation of the electric charges when the internal terrestrial masses are subject to strong compressive stress for piezoelectric effect. If the separation of the electric charges takes place on very large masses, intense electric fields are produced so to generate strong electric potential differences. If these differences are higher that the dielectric rigidity of the materials, a strong disruptive discharge can occur between the terrestrial masses. The destruction of some masses allows other masses to move generating intense seismic waves. The discharge produces the rumble and electromagnetic waves with frequencies depending on the dimensions on the focus. The tables show that the calculated frequencies (ultra-audible vibrations) are 35, 23, 17, 14, 12 kHz. (This abstract was published on Bulletin of S.I.F. on 10 September 1982, N. 127).     

MedNet: the very broad-band seismic network for the Mediterranean

Summary MedNet is the very broad-band seismographic network installed by the Istituto Nazionale di Geofisica (ING) in countries of the Mediterranean area, with a final goal of 12–15 stations and a spacing of about 1000 km between stations. The project started in 1987 and will be completed within 1992. MedNet is motivated both by research interest and by seismic hazard monitoring; it will allow to define the structure of the Mediterranean region to a high detail, to study properties of the seismic source for intermediate and large events, and to apply this knowledge to procedures of civil protection. To reach its goals, the network has been designed following the highest technical standards: STS-1/VBB sensors, Quanterra 24 bits A/D converters with 140 dB dynamic range, real-time telemetry. Five sites are now operational in Italy (L'Aquila, Bardonecchia and Villasalto) and in northern African countries (Midelt, Morocco; Gafsa, Tunisia); other sites are under construction in Pakistan (Islamabad), Irak (Rutba) and Egypt (Kottamya), while locations are examined for stations in Greece, Jugoslavia and Algeria. The centre of the MedNet network is the Data Center (MDC) in Rome; its tasks include data collection, verification, quality control, archival and dissemination, monitoring of station performance, event detection, routine determination of source parameters. Data distribution will follow the guidelines set by FDSN, and will be coordinated with other international network projects.     

A digital recording system of electromagnetic emissions

Summary A new equipment able to reveal the electric component of electromagnetic emission and suitable for underground deployment has been made. The system enables to measure the absolute value of integrated voltage of signals. Data are recorded by a solid-state memory circuit. The system is performed as a plug-in modular design and it can be also used in diverse fields of application.

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Riassunto è stata realizzata una nuova strumentazione per la rivelazione della componente elettrica delle emissioni elettromagnetiche in laboratori sotterranei. Il sistema è in grado di misurare i valori assoluti della tensione integrata dei segnali. I dati vengono registrati su un circuito di memoria a stato solido. Il sistema è stato realizzato con caratteristiche modulari e può essere utilizzato anche in altri campi di applicazione.

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Резюме Сконструировано новое оборудование для регистрации электрической компоненты электромагнитных излучений в подземных лабораториях. Система позволяет измерять абсолютную величину суммарного напряжения сигналов. Данные регистрируются в схеме с твердотельной памятью. Предложенная система собрана на специальных сменных модулях и может быть использована для различным прикладных задач.

     

Automation of seismic network signal interpolation: an artificial intelligence approach

Summary After discussing the current status of the autonomation in signal interpretation from seismic networks, a new approach, based on artificial-intelligence tecniques, is proposed. The knowledge of the human expert analyst is examined, with emphasis on its objects, strategies and reasoning techniques. It is argued that knowledge-based systems (or expert systems) provide the most appropriate tools for designing an automatic system, modelled on the expert behaviour. To speed up publication, the authors of this paper has agreed to not receive the proofs for correction.     

Some possible precursors of the main earthquakes of the Tornimparte (Central Italy) seismic sequence occurred in 1985

Summary Two tiltmeters installed at Peschiera site (Central Italy) generally showed trends that differ from the ones obtained at the network located in the Apennine region of Central Italy. Detrended tilt recordings reveal the presence of an anomalous variation during the first months of 1985. We propose to interpret this anomaly as a precursor of the main earthquakes of the seismic sequence occurred at Tornimparte area (Central Italy). The results of the deep-resistivity measurements obtained from June 1983 to December 1985 at Pizzoli area (Central Italy) reveal anomalous resistivity changes occurred at the end of May 1985. We propose that also this anomalous variation is connected with the Tornimparte seismic sequence.

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Riassunto Due inclinometri installati in località Sorgenti del Peschiera (Italia Centrale) hanno evidenziato andamenti in generale diversi rispetto a quelli ottenuti dalla rete inclinometrica situata nella regione appenninica dell'Italia Centrale. Le tracce filtrate hanno messo in risalto la presenza di una variazione anomala verificatasi nei primi mesi del 1985. Si propone d'interpretare questa anomalia come precursore dei terremoti principali della sequenza sismica avvenuta nella zona di Tornimparte (Italia Centrale). I risultati delle misure di resistività profonda ottenuti da giugno 1983 a dicembre 1985 nell'area di Pizzoli (Italia Centrale) hanno evidenziato una variazione anomala di resistività alla fine di maggio 1985. Si propone che anche questa anomalia sia connessa alla sequenza sismica di Tornimparte.

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Резюме Показания двух инклинометров, установленных в Пескиере (Центральная Италия) обычно отличаются от данных, полученных на станциях в Апеннинах Центральной Италии. Анализ данных обнаруживает аномальное отклонение в первые месяцы 1985 года. Мы предлагаем интерпретировать эту аномалию как предвестник главных змелятрясений сейсмической последовательности, наблюдавшейся в области Торнимпарте (Центральная Пталия). Результаты измерений глубинного сопротивления, полученные с июня 1983 г. по декабря 1985 г. в области Пиццоли (Центральная Италия), обнаруживают аномальные изменения сопротивления в конце мая 1985 г. Мы предполагаем, что это аномальное изменение также связано с сейсмической последовательностью в области Торнимпарте.

     

The Messina Straits tsunami of December 28, 1908: a critical review of experimental data and observations

Summary We examine the tsunami which occurred on December 28, 1908, in the Straits of Messina. We collect and review a wide set of data coming from a number of sources in order to get a picture as clear as possible of the generation and evolution of the event. We estimate the tsunami magnitude according to the Murty-Loomis scale, based upon the evaluation of the initial wave disturbance energy.

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Riassunto L'articolo prende in esame il maremoto che colpí lo stretto di Messina la notte del 28 Dicembre 1908. Si passano in rassegna criticamente i dati provenienti da numerose fonti, con l'intento di ottenere un quadro chiaro e non contraddittorio dell'evento. Al termine si propone una stima della magnitudo del maremoto secondo la scala Murty-Loomis, in stretta relazione con l'energia totale posseduta dall'onda al momento della generazione.

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Резюме Мы исследуем дунами, которые имели место 28 декабря 1908 года в Мессинском проливе. Мы собрали и проанализировали данные из ряда источииков, гтобы воссоздать картиину возможного образования и эволюции события. Мы оцениваем магнитуду цунами по шкале Мурти-Лумиса, основываясь на оценке полной энергии, запасенной в волне в момент образования.