Paolo Gasperini

CPTI11, the 2011 version of the Parametric Catalogue of Italian Earthquakes

CPTI11 updates and improves the 2004 version of CPTI with respect to background information and structure. It is based on updated macroseismic (DBMI11; Locati et al., 2011) and instrumental databases; it contains records of foreshocks and aftershocks; for some offshore events, macroseismic earthquake parameters have been determined by means of the method by Bakun and Wentworth (1997); when both macroseismic and instrumental parameters are available, the two determinations and a default one are provided (in this case, the epicentre is selected according to expert judgement, while Mw is obtained as a weighted mean); for some events, whose macroseismic data are poor, no macroseismic parameters have been determined. CPTI11 does not include the results of some methodological developments performed in the frame of the EC project “SHARE”. It does not consider the information background provided by: Molin et al. (2008); Camassi et al. (2011); recent studies on individual earthquakes; ECOS 2009 (Faeh et al., 2011) and SisFrance, 2010, yet, which will be considered in the next version. The area covered by CPTI11 is slightly reduced with respect to the one of CPTI04 (Fig. 1). The catalogue is composed of two sections: the main one (1000-2006) and the “Etna” earthquakes, for which a specific calibration is used for determining earthquake parameters. Appendix 4 supplies the list of the events which were included in CPTI04 but not in CPTI11 and the relevant explanation.

The SHARE European Earthquake Catalogue (SHEEC) 1000–1899

In the frame of the European Commission project “Seismic Hazard Harmonization in Europe” (SHARE), aiming at harmonizing seismic hazard at a European scale, the compilation of a homogeneous, European parametric earthquake catalogue was planned. The goal was to be achieved by considering the most updated historical dataset and assessing homogenous magnitudes, with support from several institutions. This paper describes the SHARE European Earthquake Catalogue (SHEEC), which covers the time window 1000–1899. It strongly relies on the experience of the European Commission project “Network of Research Infrastructures for European Seismology” (NERIES), a module of which was dedicated to create the European “Archive of Historical Earthquake Data” (AHEAD) and to establish methodologies to homogenously derive earthquake parameters from macroseismic data. AHEAD has supplied the final earthquake list, obtained after sorting duplications out and eliminating many fake events; in addition, it supplied the most updated historical dataset. Macroseismic data points (MDPs) provided by AHEAD have been processed with updated, repeatable procedures, regionally calibrated against a set of recent, instrumental earthquakes, to obtain earthquake parameters. From the same data, a set of epicentral intensity-to-magnitude relations has been derived, with the aim of providing another set of homogeneous Mw estimates. Then, a strategy focussed on maximizing the homogeneity of the final epicentral location and Mw, has been adopted. Special care has been devoted also to supply location and Mw uncertainty. The paper focuses on the procedure adopted for the compilation of SHEEC and briefly comments on the achieved results.

Identifying different regimes in eruptive activity: An application to Etna volcano

The objective identification of different regimes in the eruptive time-history of a volcano is crucial to the understanding of its physics. While a problem well-known in statistical literature under the name of change-point or scan-point problem, no method of general applicability exists for the identification of different regimes in a time-series. In particular, the available techniques seem unsuitable to the volcanological case. We developed an original procedure based on two-sample Kolmogorov-Smirnov statistics which offers satisfactory accuracy in a broad range of conditions with a minimum of assumptions and is expressly tailored to the study of geophysical phenomena. Our procedure requires neither the a priori knowledge of the number of regimes nor of the statistical distributions governing the whole process, which can be of different type. The parent distribution of each regime is inferred through a goodness-of-fit test, and this in turn allows the confidence intervals for each of the change-points identified to be estimated by numerical simulation. This procedure is applied to the eruptive history of Mount Etna volcano. Available data allow the analysis of flank eruptions in the period 1600–1980, while the total output (summit and flank activity) can be studied only in the period 1971–1981. Information on eruptive history can be therefore obtained at two different timescales. Since no univocally accepted catalog exists except for the last few decades, we use two different sets of data, which practically exhaust all the available information. The results are interpreted by a stability analysis, and only stable results are retained. Our analysis yields that: • - The inter-event times of flank eruptions in the period 1600–1980 follow two regimes before and after year 1865, while the eruptive activity in the period 1971–1981 follows four different regimes. In each regime eruptions occur according to a Poisson process and Etna behaves as a random nonstationary volcano both at long (few centuries) and short (few years) time-scales. The eruptions appear therefore to be triggered by several combining effects with a balance showing fluctuations at both time-scales. • - The volume output of flank eruptions in the period 1600–1980 follows three different regimes, with change-points at 1670 and 1750. The volume output in the period 1971–1981 follows a single regime. Least squares regression and the related confidence bounds, calculated for each regime, suggest that, even accounting for summit activity, the output rate in the period 1971–1981 is not anomalously high. Provided that no further change in regime takes place, the confidence bounds can be used to cast estimates on the expected future activity. • - The series of the mean effusion rates (erupted volume/duration of the eruption) applied to flank eruptions in the period 1600–1980 follows two different regimes, with a change-point around year 1950. There is a net decrease in the mean effusion rate from over 24 m3 s−1 to about 7 m3 s−1, which suggests a change in the eruptive style to lower mean effusion rates. The total output (flank + summit) data of the period 1971–1981 confirms this issue, with averaged mean effusion rates lower than 12 m3 s−1. • - The points of change in regime in the time-series of the inter-eruption times and volume outputs do not coincide, thus implying that eruptions are governed by other factors than the input of magma. At the same time, the analysis of seismic activity does not suggest the stress field as a most important factor. The eruptive activity does not appear to be controlled by a single factor, but by the balance of several contributing factors, further corroborating the conclusion that Etna behaves as a random nonstationary volcano. • - The relatively small fluctuations in each of the periods identified in the flank output series suggest a constant input within each output regime, although the unavailability of both a reliable model and accurate estimates on historical summit eruptions recommends prudence in accepting this conclusion. • - There appears to be no significant correlation between the volume of a “large” flank eruption and the subsequent inter-event time. This, with the above proviso, suggests the absence of any high-level magma reservoir.

Local magnitude revaluation for recent Italian earthquakes (1981–1996)

In the framework of a joint project of theItalian Gruppo Nazionale per la Difesadai Terremoti (GNDT) and the IstitutoNazionale di Geofisica (ING), devoted tothe reorganization of the Italianearthquake instrumental database from 1981to 1996, we approached the problem of thehomogeneous determination of localmagnitude in Italy. As a first step, webuilt a database of real Wood-Andersonamplitudes deduced from the available dataof the two instruments that were inoperation in Italy up to 1989 as well as ofsimulated Wood Anderson amplitudes computedby Very Broad Band recordings, availablesince 1990. The simultaneous computation ofthe attenuation function together with themagnitudes and the station residuals allowsus to verify that, for the Italian area,this function does not significantly differfrom the original one given by Richter. Inthe second step, the so obtained Mlmagnitudes are used as a reference data setto estimate a new empirical relation forthe duration magnitude Md using the unifiedphases database of the Italian NationalSeismic Network (RSNC) of ING and of themost important local seismic networksoperating in Italy. The same data set wasalso employed to calibrate magnitude Mabased on amplitudes coming from shortperiod vertical seismograms recorded by theRSNC automatic acquisition system. At lasta set of reasonable criteria to choose themost reliable among Ml, Md and Ma has beenformulated. The resulting set of magnitudesproved to be definitely better calibratedthan the one obtained by procedures in useat RSNC.

The Attenuation of Seismic Intensity in Italy: A Bilinear Shape Indicates the Dominance of Deep Phases at Epicentral Distances Longer than 45 km

The attenuation of seismic intensity with distance in Italy is analyzed by using felt intensity report data obtained from two comprehensive historical databases recently made available. The observed attenuation pattern that in the past was interpreted as a logarithmic or root (square or cubic) attenuation law shows quite clearly two different linear trends in the near and in the far field. At distances shorter than 45 km, the decrease of the intensity with distance is about one degree per 20 km, while at longer distances the slope is about one degree per 50 km. This is in agreement with some recent findings of realistic modeling of seismic ground motion that has been explained as the transition from upper-crust direct Sg phases to waves reflected at the Moho controlling the energy main release. The slope of the curve in the far field shows a regional dependence in agreement with recent works on the attenuation of Pn and Sn phases in Italy. If effective, this correlation might allow us to discriminate the contribution of crustal and subcrustal paths in seismic intensity attenuation studies. Manuscript received 31 May 2000.

Contour mapping of Italian seismicity

Abstract The scope of the present work is to identify the Italian seismic regions, toward a better definition of the active tectonic structures. Spatial filtering is used, together with the recently released PFG-ENEL seismic catalog which covers the period 1000–1980. Any such approach based on catalog data has to acknowledge that catalog reliability and resolving power are functions of time and position. These problems, which can potentially lead to an incorrect regionalization, can be attributed to catalog incompleteness. The effects of the latter are estimated and correlated through a new approach, which determines the completeness interval from the plot of the cumulative number of events versus time, and measures the degree of incompleteness by assuming it to be a function with a continuous first derivative. In this way, all the information present in the catalog can be used in contour mapping by an appropriate weighting of incomplete parts in spatial filtering. On the other hand, the choice of the weight factors involves some arbitrary judgement and therefore introduces a bias. In order to reach an objective result, different weighting schemes covering all feasible choices are tried, and the final regionalization is concluded to be valid only if it is stable. A fair stability is obtained and it is henceforth possible to conclude that the seismic regions identified represent an unbiased picture of the real situation. Interestingly, different areas exhibit a different seismic character, some being capable of frequent activity but never exceeding moderate magnitude values, and others being characterized by a scarcity of moderate events combined with the capability of occasional large earthquakes.

A database of revised fault plane solutions for Italy and surrounding regions

The analysis of fault plane solutions of earthquakes is carried out in most seismotectonic studies to characterize the tectonic deformation styles and to estimate strain and stress directions in the investigated areas. Nevertheless the data available in the literature, are reported with different formats and notations and, in most cases, only in papery form, so that they are not suitable to be handled by computer procedures and graphic packages. Sometimes the data are reported with typographical errors, inaccuracies and inconsistencies that make them almost useless for other investigators. In some cases several solutions, often very different among each other, are given for the same earthquake by different authors thus requiring a choice be made among them. We have tried to solve some of these problems, in building a comprehensive database, on a Microsoft ACCESS platform, including most of the mechanisms (presently about 5000) published for the Italian region and more generally for the Mediterranean area. We tested the perpendicularity of nodal planes and/or P and T axes of all solutions and, when both axes and planes are given, even their mutual consistency. Moreover from the comparison of planes and axes we were able to detect and sometimes to correct misprints and other types of errors. All the parameters are recomputed uniformly and consistently, keeping track of all the corrections made. We also established an automatic procedure, based on several criteria, to choose the most “representative” solution when more than one is available for the same earthquake. The MS-ACCESS application also allows to making selections on the earthquake data, to display the plot of the mechanisms and to export data files suitable to be handled by graphic software and user written procedures.

Pattern recognition applied to volcanic activity : identification of the precursory patterns to Etna recent flank eruptions and periods of rest

Abstract Computational pattern recognition is an invaluable tool in understanding the phenomenology of complex processes and represents the first step towards their effective physical modeling. So far it has never been used in volcanology. We discuss in detail pattern recognition algorithms of the “logic” type and present an application to the recent eruptive activity of Mount Etna volcano. The specific aim is a characterization of the intermediate-term precursory patterns to its flank eruptions. A comparatively successful recognition is obtained, providing the combinations of parameters which have been precursory to eruptions and periods of rest in the last fifteen years. The recognized patterns yield two main results: (a) the seismicity in the Gulf of Patti is identified as the most important precursor, and a further correlation study confirms this issue as highly significant, implying that regional tectonic stress, and in particular the structures around the Tindari-Giardini lineament, play a fundamental role in triggering Etna flank activity; (b) an operative prediction-oriented application of the recognized precursory patterns is tentatively possible.

Statistical identification of physical patterns which accompany eruptive activity on Mount Etna, Sicily

Abstract A new statistical nonparametric pattern recognition algorithm is used to identify the phenomenology which accompanies summit and flank eruptions on Mount Etna, Sicily. This algorithm allows us to solve some of the operational problems typical of logic-type pattern recognition algorithms. Volcanic activity is parametrized through 12 variables concerning seismicity, past eruptive history, and precipitation, which practically exhaust the presently available data. In the 40 days which precede and follow the onset of each eruption, we identified no pattern whatsoever for summit eruptions, and a single significant pattern for flank activity. This indicates different eruptive mechanisms for flank and summit events. The latter appear to be independent of all the phenomena considered, and should therefore be ascribed either to magma feeding processes, a variable which we were not able to consider in our analysis due to the lack of data, or to random behaviour, without any repetitive scheme. Flank activity appears to be linked to the state of regional tectonic stress, but is independent of past eruptive history and groundwater level. This means that eruptions of the size Etna recently experienced, do not perturb the system, which must have a much larger capacity, at least of the order of 10 9 m 3 .

Reproducing the velocity and stress fields in the aegean Region

Recent satellite geodetic measurements help to clearly define the velocity field in the Aegean-Anatolian area. The velocity field can be broadly characterized by anticlockwise rotation of this region relative to Eurasia, around a pole located at Lat. 32.73, Long. 32.03, north of the Egyptian shoreline. Studies of the fault kinematics in the region also provide information on the time evolution of the stress field. In this work, we model deformation in the Aegean-Anatolian region to better understand the tectonic origin of the observed stress and velocity fields. We found that the observed deformation pattern can be well reproduced by imposing simple boundary conditions including: (1) northward displacement of the Arabian plate, (2) locking of eastward motion in northwestern Greece and (3) suction force at the Hellenic trench. The observed variation in the stress field occurred at 0.9 Ma can be partially explained by a change in the activity of the North Anatolian fault.