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S260 Int J Earth Sci (Geol Rundsch) (2010) 99 (Suppl 1):S243–S264

Fig. 5 Geometry and average seismic velocity tensor of the Adriatic relationships between the local coordinate reference system and the
Basal Thrust (ABT), Sicilian Basal Thrust (SBT) and Southern Cartesian coordinate system, as defined by Aki and Richards (1980),
Tyrrhenian Compressional (STC) seismotectonic provinces. The maps are also shown. The upper table reports parameters and results of the
report in grey the schematic area of the three provinces and the vertex calculation of the velocity tensors, through application of Kostrov’s
of the corresponding polygons; the black arrows give the direction of (1974) procedure: L1, L2 and L3 length, width and thickness of the
the horizontal contractional component (k 1 ) of the average strain seismogenic volume; M smax = magnitude of the maximum observed
tensor calculated from the focal mechanisms in Table 2. The block event; _ M o = moment rate); k1, k2 and k3 = computed eigenvectors
diagram gives a sketch of the wedge shape assumed for the ABT in mm/year with trend and plunge. The lower table reports the
and SBT seismogenic volumes (L1 length measured along-strike, components of the strain rate and of velocity tensors; positive and
L2 surface width, L3 average seismogenic thickness); the spatial negative values indicate compression and tension, respectively

component (k 2 ) and a vertical (k 3 ) component. Seismic direction across northern Italy. No error computation was
shortening happens at a rate of *0.3 mm/year in an forwarded and the adopted boundaries of the seismotec-
average WSW–ENE direction across the ABT province, tonic regions were very large, and not geologically con-
*0.1 mm/year in an average N–S direction across the SBT strained. The Sicilian domain included onshore and
province and *0.2 mm/year in an average NNW–SSE offshore seismicity and the northern Apennine domain was
direction across the STC province. also comprehensive of Padanian and Southern Alps
In the previous literature, a SW–NE shortening rate in regions. More recently, Jenny et al. (2006) have calculated
the range of 0.3–0.5 mm/year was computed by Westaway distinct shortening rates for the offshore and onshore
(1992) for the compressional regions of the northern Sicilian compressional provinces, but the boundaries
Apennines, based on analysis of the historical earthquake adopted for the zones are different from ours. In fact, they
record, but the eastern Marche–Adriatic region considered did not consider the presence of the Peloritani–Nebrodi
here had not been analysed in detail and, in any case, the extensional domain of northern Sicily which is interposed
strain rate and velocity tensors had not been calculated. between mainland-southern Sicily and the Southern
These values were computed by Kiratzi (1994), who Tyrrhenian compressional domains. Therefore, they
obtained shortening rates of 1–2 mm/year in the N–S enlarged northward the mainland Sicily domain. In any
direction across Sicily and 2–3 mm/year in the SW–NE case, their results are comparable with those obtained here,

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