Contour mapping of seismic areas by numerical filtering and geological implications

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Materials for the catalogue of Italian earthquakes: A reappraisal of minor seismicity

Nel catalogo CPTI04 [Gruppo di Lavoro CPTI, 2004], un numero consistente di terremoti è tutt’ora privo di uno studio di riferimento recente. Nel corso di questo lavoro sono stati studiati 851 di questi terremoti: si tratta di eventi con Io tra il V-VI e il VII grado MCS, verificatisi dal 1198 al 1980 ma soprattutto nel Novecento, i cui parametri epicentrali derivano dal catalogo PFG [Postpischl, 1985a]. Questi eventi sono stati sottoposti a una sistematica revisione, adottando una procedura speditiva omogenea e rigorosa che ha permesso di elaborare nuovi parametri per 741 su 851 terremoti studiati. Nei restanti 110 casi lo studio ha portato a riconoscere 26 degli eventi studiati come inesistenti o estremamente dubbi. In 84 casi, infine, le informazioni storiche raccolte non sono risultate sufficienti per l’elaborazione di nuovi parametri. Il valore di intensità epicentrale è diminuito nel 72% dei casi e aumentato solo nel 4.5% di essi; il 50 % circa dei terremoti rivisti ha un’intensità epicentrale inferiore alla soglia attualmente adottata dal catalogo. Si notano anche significative variazioni nella localizzazione di alcuni dei terremoti rivisti. I risultati del lavoro sono riassunti in 851 schede di sintesi e circa 12.500 punti d’intensità osservati, che sono presentati in questo Quaderno insieme a una sintetica introduzione metodologica

Materiali per un catalogo dei terremoti italiani: eventi sconosciuti, rivalutati o riscoperti

The large-scale studies of historical seismology carried out in Italy and Europe in the last decades were mostly aimed at improving knowledge about earthquakes that were already listed in the extant parametric catalogues, rather than at identifying earthquakes that were not listed in them. From 1992 onwards, some of the authors of this study started to look for such “forgotten” earthquakes in different ways (by systematic surveys of serial historical sources, or by extensive investigation of local records in selected areas). More than 2000 pieces of evidence related to as many earthquakes not listed by any seismological compilations/catalogues were thus identified. In 2003 all resources were pooled in a common effort, meant to complete the revision of minor “known” earthquakes carried out by Molin et al. [2008] with a study of the most relevant “unknown” earthquakes identified so far. We present here the results of the analysis of 227 damaging earthquakes, 155 of which are “unknown” to the seismological tradition. Other 72 events were listed in the Postpischl [1985] catalogue, but not in newer parametric catalogues, no evidence of damage being available for them at the time: such evidence has now been found and, in 21 cases at least, it allows for a significant re-evaluation of macroseismic intensity

Contour mapping of seismic areas by numerical filtering and geological implications

A method is described that makes possible the identification of the independent seismic units of a given area (Caputo and Postpischl, 1973 b). The seismic information is treated as a bidimensional signal disturbed by a certain background noise. The filtering of this noise makes it possible to delineate the seismic areas objectively. An indirect check on the method was made by estimating with respect to the various regions identified the a and /J parameters of the law Ny = a e~Py which gives the number of earthquakes with magnitude (intensity) greater than or equal to y

Le conoscenze attuali dei movimenti del suolo nell'area italiana. Proposte per un coordinamento delle ricerche in atto in considerazione delle nuove strumentazioni e tecniche operative.

The significance of monitoring crustal deformations related to variousgeophysical phenomena is pointed out; both classical geodetic methodsand modern spatial techniques are reviewed. The analysis of thestate of the art in Italy is carried out with particular concern to surveysin seismic and volcanic areas

Palaeoseismicity from karst sediments: the “Grotta del Cervo” cave case study (Central Italy)

Karst speleothems can be used for tectonic and palaeoseismic analyses; in particular, stalagmites can be treated as the records of a natural pendulum. Samples of stalagmites from the “Grotta del Cervo” and the “Grotta a Male” caves (Central Italy) have been dated using 14C and U/Th radiometric methods. The present paper shows the limits and validity of such methods for dating strong earthquakes of the past. In particular, radiometric 14C dating shows that the youngest general stalagmitic collapse observed inside the “Grotta del Cervo” cave must be related to the December 1456 earthquake of Central Italy