ASMI Archivio Storico Macrosismico ItalianoItalian Archive of Historical Earthquake Data

In tectonically active areas, such as the Italian peninsula, studying the faults responsible for strong earthquakes is often challenging, especially when the earthquakes occurred in historical times. In such cases, geoscientists need to integrate all the available information from historical reports, surface geology, and geophysics to constrain the faults responsible for the earthquakes from a seismotectonic point of view. In this paper, we update and review, according to the EMS-98 scale, the macroseismic fields of the five main events of the 1783 Calabria sequence (5, 6, and 7 February, 1 and 28 March, Mw 5.9 to 7.1), two other destructive events within the same epicentral area of the 1783 sequence (1791, Mw 6.1 and 1894, Mw 6.1), plus the Messina Strait 1908 earthquake (Mw 7.1). For the 1783 seismic sequence, we also elaborate an updated and new catalog of coseismic effects. The new macroseismic fields were analyzed using a series of MATLAB algorithms to identify (1) the unitarity of the field or its partitioning in sub-sources and (2) the field and sub-fields’ main elongation. A collection of earthquake scale laws from literature was used to compute the average source parameters (length, width, and area) with their range of variability, and an elliptical map-view representation of the source geometry was calculated and made available. The analyses of such data allow us to speculate on the earthquakes/faults association, as well as propose new interpretations and reconstruct the space–time evolution of the significant southern Calabria seismic sequences in the last five centuries.

We present the results of an Italian­Maltese research, carried out to collect the macroseismic data needed to update the seismic catalogue of the Maltese Islands [Galea, 2007]. In this work we adopted the most up­to­date criteria developed by Italian historical seismology, obtaining results that significantly improve knowledge, particularly for the 1650­1923 time­window. Several previously unknown local earthquakes have been identified and evidence has been found of earthquake damage caused to the Maltese Islands both by earthquakes probably located in the Sicilian Channel (1658, 1780, 1861), and by some strong Greek earthquakes (1756, 1810, 1846). The European macroseismic scale 1998 (EMS­98, Grünthal [1998]) was used to assign macroseismic intensities. Basic information on seismic­induced natural phenomena (landslides, tsunamis) was also collected, to be used as a further constraint on the location and size of associated earthquakes, or for paleoseismological studies. As an added bonus, the study collected evidence of some Sicilian earthquakes unknown to seismological literature and data useful to improve the macroseismic database of already known Sicilian and Greek earthquakes.

The Catalogue lists earthquakes that occurred in Italy between 461 B.C. and 1997, and earthquakes that occurred in the general Mediterranean area between the VIII century b.C. and the XV century. This version (CFTI5Med) features: the retrieval and formatting of over 23,000 original bibliographic documents, transcribed or printed, nearly 50% of those utilized in the CFTI5Med. These documents are now available on-line as fully searchable pdf files; a full geological reinterpretation, georeferencing and reprocessing of over 2,300 descriptions of earthquake-induced environmental effects, which are now all available and searchable in a user-friendly web-GIS environment; the elaboration of a number of texts and commentaries that were missing from the CFTI4Med version of the catalogue; a totally re-designed and more efficient web- and web-GIS interface. The new Catalogo dei Forti Terremoti in ltalia includes 1,259 earthquakes that occurred in Italy (98 of which are currently considered false). No commentaries on the main earthquake effects were available in the previous version of the catalogue for 87 of such events as they had not been updated with respect to the information supplied in Guidoboni e Comastri (2005) for the 1000 AD-1500 AD time interval. The commentaries concerning the most significant effects of Italian medieval earthquakes have now been elaborated and are available along with the information on more recent events. For the remainder of the earthquakes first presented with the CFTI4Med - those that occurred in the general Mediterranean area away from the Italian coasts - the new catalogue provides only the felt reports and basic epicentral parameters.

The macroseismic studies of historical earthquakes have become, in recent years, of great interest and the Italian Geodynamic Project has promoted and encouraged them.

This renewed interest induced us to complete the researches on the seismicity of Sicily and Calabria -which started with the earthquake catalogue, Carrozzo et al (1975)- by compiling a catalogue of isoseismal maps for earthquakes which occurred in the period 1783-1978.

Data, already gathered during the preparation of the earthquake catalogue, have now been critically reinterpreted, so making possible the drawing of isoseismal maps of 142 events. Later on, as established among members of group «catalogo dei terremoti», a macroseismic study of earthquakes preceding 1783, with intensity greater than nine, will be carried out trying to find other original references and papers of contemporary authors.

The quality of data is not homogeneous. Only earthquakes of greater intensity have a remarkable number of information, nevertheless, earthquakes which had a poorer quality of information, but enough to define the macroseismic field, were included as well.

Criteria used in the catalogue

The degree of intensity has been assigned using the M.S.K.-64 scale.

This scale shows the advantage of giving separate criteria of assessment of the intensity, according to the description of three kinds of effects:

1. on buildings and man-made structures,
2. on ground and in the regime of ground water,
3. on people and their environment.

This permits the definition of the intensity with a good accuracy even when there are poor descriptions of the effects as often happened for old or low-intensity earthquakes.

The original description of damage by past authors, have been reinterpreted according to criteria of the M.S.K. scale; when this was not possible, due to lack of descriptions, the values of intensity, generally expressed according to the Mercalli scale, have been transformed into the corresponding M.S.K.-64 values, using the relationship.

I_M.S.K. = 0.94 I_M.M. + 0.08 (Cosentino-Lombardo, 1980)

As regards criteria used in drawing isoseismals, a simple contouring of points representing the estimated intensity was performed, this avoids any normalization of the macroseismic field and any subjective interpretation.

In some cases, mainly for events located in the etnean area, when there was lack of descriptions but it existed the isoseismals map drawn by the author according to his own survey, the mesoseismal area was faithfully reported.

The isoseismals of studied events have been grouped into 5 zones Calabria and Peloritani area, Sicilian coastal chain, Etna, Iblei and Belice with different seismic and structural characteristics, according to the preliminary results of studies on the seismotectonic zonation of Sicily and Calabria (Barbano et al., 1978; Barbano et al., in print).

The map in fig. A, besides, shows the macroseismic epicentres, estimated as barycentre of the mesoseismal area. The epicentres of earthquakes occurred in the sea were included as well, only if the trend of isoseismals allowed a rough location.