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06 133-20 06(209-222) 25-06-2007 14:24 Pagina 215

SEISMOGENIC EVIDENCE OF ONGOING COMPRESSION IN EASTERN-CENTRAL ITALY AND MAINLAND SICILY: A COMPARISON 215

Table 2b
Major crustal earthquakes (magnitude moment ≥≥ ≥≥ 5.0) above the Sicilian Basal Thrust from 217B.C. to 2005 A.D.
H Depth
n° Y M D H M Lat Lon Locality References Imx Io Maw Mw SP
(km) range
1 17 37.8 15.2 D Reggio C.-Sicil. CFTI 85 85 5.14 DC
2 361 37.5 14 D Sicilia CFTI 100 100 6.6 DC
3 1536 3 23 37.502 15.087 S-Et Catania DOM 65 65 5.03 EV
4 1578 37.508 13.083 S Sciacca DOM 70 70 5.17 SC
5 1624 10 3 17 37.27 14.75 S Mineo CFTI 90 80 5.57 SC
6 1643 7 17 37.783 14.599 S Troina DOM 65 65 5.03 T
7 1716 12 1 37.502 15.087 S Catania DOM 70 70 5.17 SC
8 1718 2 20 37.599 14.619 D Sic. Or. (Regalbuto) DOM 65 65 5.4 DC
9 1740 6 13 37.582 12.84 S Sciacca DOM 75 75 5.37 SC
10 1818 2 20 18 15 37.6 15.13 D Catanese CFTI 95 90 6 DC
11 1822 4 6 37.747 14.398 S Nicosia DOM 65 65 5.03 T
12* 1823 3 27 37.931 12.329 D Favignana R99 70 70 5.17 DC
13* 1828 5 18 37.8 12.433 D Marsala R99 70 70 5.17 DC
14* 1865 7 19 1 37.702 15.153 S-Et Area Etnea ABAR2000 90 90 5.03 EV
15* 1878 10 4 0 46 37.266 14.691 S Mineo ABAR2000 65 65 5.03 SC
16 1907 5 8 37.5 15 S-Et Catania sud POS85 70 5.17 EV
17* 1914 5 8 18 1 37.659 15.149 S-Et Area Etnea ABAR2000 95 95 5.3 EV
18 1934 9 11 1 19 37.439 14.58 D Madonie DOM 65 65 5.03 DC
19* 1959 12 23 9 29 37.428 14.89 D Piana di Catania ABAR2000 65 65 5.23 U
20* 1968 1 14 12 28 37.804 13.012 19 D Valle del Belice A&J87 5.2 DC
21* 1968 1 14 13 15 37.676 12.966 1 S Valle del Belice A&J87 5.1 DC
22* 1968 1 15 1 33 37.817 13.006 34 D Valle del Belice A&J87 5.2 DC
A&J87 5.5
23* 1968 1 15 2 1 37.75 12.983 13 D Valle del Belice DC
CPTI04 6.12
24* 1968 1 16 16 42 37.857 12.976 36 D Valle del Belice A&J87 5.2 DC
25* 1968 1 25 9 56 37.687 12.966 3 S Valle del Belice A&J87 5.2 DC

seismic section (BELLO et alii, 2000) and the WARR sec- example the 1968 Belice and 1972 Ancona seismic
tion across eastern Sicily (CHIRONI et alii, 2000) (see sequences, these values are substantially different. This
traces of the sections in fig. 1c). may be inferred on one side to the possible low reliability
of the earthquake parameters calculated in the early instru-
mental period and on the other side to the difficulties in
4. MAJOR EARTHQUAKES the evaluation of the intensity of single events belonging to
seismic sequences because of cumulative damage effects.
In order to have the most possible complete picture For all the selected events, we have attempted to valu-
on the major earthquakes that have occurred in historical ate the depth range of the seismogenic source. We fixed
and present times within the surface areas above the 0-to- two depth ranges from geological considerations, an upper
30 km ABT and SBT depth contour lines (grey areas in crust range (<~10 km), labelled S (Shallow), and a mid-to-
fig. 2), we compiled an integrated dataset of the seismic lower crust one (10-30 km), labelled D (Deep), and we
events with magnitude moment ≥4.5 for the time interval chose the appurtenance of each earthquake to one or the
217 B.C.-2005 A.D.. The main source of data was the other of the two ranges through the analysis of the shape
CPTI04 parametric catalogue, which contains informa- and extent of the macroseismic field (BARATTA, 1897;
tion on the Italian historical earthquakes from 217 B.C. to POSTPISCHL, 1985; MONACHESI & STUCCHI, 1997; BOSCHI
2002 (WORKING GROUP CPTI, 2004); it was integrated et alii, 2000). Simply speaking, we looked at the distance
and updated with data from other regional catalogues and difference in intensity between the macroseimic epi-
(BARATTA, 1897; POSTPISCHL, 1985; MONACHESI et alii, centre and the other data points¸ also taking into consider-
1985; MONACHESI et alii, 1991; DOM by MONACHESI & ation the year of occurrence and the geographic location,
STUCCHI, 1997; CFTI by BOSCHI et alii, 2000), from spe- e.g. the historical context. Some examples of the macro-
cific papers on reviewed historical earthquakes (RIGANO seismic fields which we defined as «shallow» and «deep»
et alii, 1999; AZZARO & BARBANO, 2000; AZZARO et alii, are shown in fig. 4. Based on indications from the macro-
2000a; AZZARO et alii, 2000b) and from regional instru- seismic catalogue of Mt. Etna (AZZARO et alii, 2000a), the
mental catalogues (Catalogo Sismico Italiano 1981-2002 earthquakes related to the volcanic dynamics (swarm
by CASTELLO et alii, 2005 and BOLLETTINO SISMICO ITA- sequences in the first 8-10 km of depth) were separately
LIANO, 2003-2005). grouped and labelled as Shallow-Etna (S-Et) in tab. 2b.
All the events of the dataset are projected onto the epi- Evidently, it was not possible to define the depth range of
centre map of fig. 2, whereas a selection of the events with all the events and the uncertain ones were labelled U.
magnitude moment ≥5 is given in tabs. 2a and 2b. The Once the events of the merged datasets were projected
magnitude moment is labelled M w when derived from onto the ABT and SBT depth-contour maps (fig. 2), exclud-
instrumental data and M aw when derived from the macro- ing the S-Et events, it was evident that earthquakes belong-
seismic field, in the case of the historical earthquakes, or ing to the shallow source group prevailed in the area corre-
through a weighted average procedure which considers sponding to the surface projection of the upper crust thrust
both the macroseismic and the instrumental information, segment (depth-contours 0-to-10 km), whereas the deep
in the case of early instrumental and instrumental events source group prevailed above the lower crust segments
(WORKING GROUP MPS, 2004). When available, we have (depth-contours 10-to-30 km). Just a few events classified
reported both the M w and M aw values in tabs. 2a and 2b. In as shallow sources were found to be located within the
the case of early instrumental earthquakes, such as for areas above the deep crust portions of the ABT and SBT.