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06 133-20 06(209-222) 25-06-2007 14:24 Pagina 212

212 G. LAVECCHIA ET ALII

TABLE 1
Parametric data of the focal mechanisms drawn in fig. 2 (events with M w ≥4.0 and depth <40 km occurring since 1968
above the ABT and the SBT).
KEY: G85=GASPARINI et alii, 1985; A&J87=ANDERSON & JACKSON, 1987; F&A=FREPOLI & AMATO, 2000; P&AL=PONDRELLI et alii, 2004;
F&A97=FREPOLI & AMATO, 1997; R89=RIGUZZI et alii, 1989; P02=PONDRELLI et alii, 2002; S03=SANTINI, 2003; C73=CONSOLE et alii, 1973.
– Parametri focali degli eventi con magnitudo momento (Mw) >4.0 e profondità <40 km a partire dal 1968. I meccanismi
relativi sono proiettati ivi fig. 2.
KEY: G85=GASPARINI et alii, 1985; A&J87=ANDERSON & JACKSON, 1987; F&A=FREPOLI & AMATO, 2000; P&AL=PONDRELLI et alii, 2004;
F&A97=FREPOLI & AMATO, 1997; R89=RIGUZZI et alii, 1989; P02=PONDRELLI et alii, 2002; S03=SANTINI, 2003; C73=CONSOLE et alii, 1973.

Strike Dip Rake Strike Dip Rake
Name Y M D Lon Lat Depth Mw Ml Ref
A A A B B B
1972 02 04 13.440 43.720 216 66 -147 112 60 -27 4.8 4.5 G85
5 C73
1972 02 04 13.370 43.730 319 83 48 128 77 -28 4.6 4.3 G85
5 C73
1972 02 04 13.360 43.720 225 63 -164 222 42 171 4.3 4 G85
Ancona 5 C73
sequence
1972 02 05 13.400 43.720 246 35 -166 145 82 -55 4.6 4.3 G85
10.4 C73
1972 02 06 13.430 43.710 212 80 -143 115 54 -11 4.6 4.3 G85
8.3 C73
1972 06 14 13.470 43.690 3 34 70 -170 301 81 -19 4.8 4.5 G85
1987 07 03 13.843 43.174 5 140 56 80 338 35 104 4.6 4.2 R89
P.S. Giorgio 1987 07 03 13.849 43.201 5 9 55 104 205 36 71 4.1 3.6 R89
sequence 1987 07 03 13.868 43.200 5 185 40 78 18 50 100 4.3 3.9 R89
1987 07 03 13.848 43.2050 5 152 60 56 25 43 134 4.3 3.9 R89
Montefeltro 1987 07 05 12.160 43.760 10 294 36 55 155 61 113 4.2 3.8 G89
Northern 1991 12 15 13.067 43.633 9.3 130 30 60 343 64 107 4.0 3.1 F&A97
Marche
Southern 1995 07 23 14.033 42.717 19.2 99 40 60 316 56 113 4.1 3.6 F&A97
Marche
Pesaro 2000 05 05 13.192 44.014 5 195 25 30 77 78 112 4.3 4.1 S03
Montegrimano 2000 08 01 12.440 43.890 18 212 28 42 84 72 112 4.3 4.5 P02

1968 01 15 12.983 37.750 13.0 270 50 90 90 40 90 5.5 A&J87
Belice
sequence 1968 01 16 12.976 37.857 36.0 250 58 80 88 33 106 5.2 A&J87
1968 01 25 12.966 37.687 3.0 270 64 85 101 26 100 5.2 A&J87
Mazara del
1981 06 07 12.470 37.670 18.1 48 29 48 274 69 110 4.9 4.4 P&Al
Vallo
Maletto 1987 08 13 15.060 37.900 35.9 352 42 -10 89 83 -132 4.8 4.3 P&Al
Nebrodi 1992 09 27 14.667 37.900 23.3 60 90 40 330 50 180 4.1 4.2 F&A
Caltanissetta 1995 04 11 13.983 37.583 8.7 170 80 30 74 60 169 4.2 4.1 F&A
Etna 1995 02 10 14.967 37.783 20.5 85 65 10 350 81 155 4.1 3.7 F&A

3. FOCAL MECHANISMS AND INSTRUMENTAL SEISMICITY JACKSON, 1987), in both cases the average P-axis being
nearly N-S and sub-horizontal. The pure thrusting solu-
A selection of the focal mechanisms available in the tion is better supported by the E-W elongation of the
literature for the events with moment magnitude ≥4.0, macroseismic field and by the northward-deepening of
which have occurred since 1968 within the ABT and the hypocentral depths, from close to the surface down
SBT surface projection areas, between the depth-con- to the base of the crust (MONACO et alii, 1996). An
tour lines 0-to-30 km (grey areas in fig. 2), is given in almost pure E-W compressional solution, is also shown
fig. 2 and tab. 1. by the 1981 Mazara del Vallo event, sited at a depth of
In central Italy, the 1972 Ancona seismic sequence about 18 km, nearly 40 km westward of the Belice main
(M max =4.8) is characterized by a prevailing strike-slip shock (fig. 2, tab. 1). The few other events located in
kinematics (GASPARINI et alii, 1985), whereas the 1987 central and eastern Sicily (1995 Nebrodi 1992, Caltanis-
Porto S. Giorgio sequence (M max =4.6) shows prevailing setta 1995 and Etna 1995) show strike-slip and reverse-
reverse solutions. All available mechanisms are compati- oblique kinematics with an average N-S trend of P-axes.
ble with NE-SW to E-W trending sub-horizontal P-axes. Furthermore, the focal mechanism inversion of the mid-
In Sicily, the focal solutions of the highly destructive to-lower crust background seismicity (Ml 2.2-3.7)
1968 Belice seismic sequence (M max =5.5) were evaluated recorded by local and national networks at Mt. Etna
either as right lateral transpression on a NNE-striking indicate nearly N-S regional compression (CASTELLANO
plane (MCKENZIE, 1972; GASPARINI et alii, 1985) or as et alii, 1997; COCINA et alii, 1997; NERI et alii, 2005) (see
pure thrusting on a north-dipping plane (ANDERSON & inset in fig. 2).