GNGTS 2014 - Atti del 33° Convegno Nazionale

basin tectonic Sulmona) the MOPS are exclusively represented by “ Stable Zone Susceptible for Local Amplification”, as well as by the presence of “Unstable Zone”. The comparative analysis between the lithostratigraphic data and those of the resonance frequencies (f0) allowed us to group the “stable zone susceptible for local amplification“in two Macrozones: 1) microzones susceptible for local amplification where f0 <1 Hz; 2) microzones susceptible for local amplification with f0 ≥ 1 Hz. Although this choice has led, almost, to a duplication of the number of micro-zones, it is justified by the fact that the areas with f0 ≥ 1 Hz have a greater engineering interest (phenomenon of double resonance). Despite this distinction has been made on point noise data and knowing that the behavior of seismic waves during an earthquake may be much more complex, we believe this solution provides a first broad grouping for the subsequent numerical modeling of micro-zones. Further to the above lithostratigraphic and geometry complexity of the buried basin, the achievement of the level 3 of MS is necessary for the presence of different zones and types of instability observed in the Sulmona area. They include the occurrence of active and capable faults along the slope of Mt. Morrone (Fig. 2), whose definition of the fault trace and expected earthquake parameters must be analyzed through detailed geological and geophysical studies and paleoseismological investigations. Problems of slope instability, due particularly to the phenomena of rock-fall from the very steep slope of the M. Morrone (Fig. 2), also emerged from studies of level 1, which require detailed surveys and geomechanical modeling. Moreover, areas susceptible to instability due to liquefaction and differential settlement have also been identified, respectively, in the recent fine alluvial sediment and in the center of Sulmona, rebuilt several times over a complex stratigraphy of superimposed Roman and medieval archaeological levels. Hints for a 2D or 3D amplification effects from earthquake records. The Italian Department of civil protection has installed four stations of the permanent strong motion network to monitor the area of Sulmona (see Fig. 2). Station SULA and SULC are installed in the centre of the plain, SULP in correspondence of a debris fan, while SUL is installed in correspondence of a rock outcrop. Three stations (SUL, SULC and SULA) have contemporarily recorded one seismic event occurred on 2013-02-16 at 21:16:09 GMT (Mw 4.9, Ml 4.8) at an epicentral distance of about 50 km. The acceleration, velocity and displacement records are obtained from the Italian accelerometric archive (itaca.mi.ingv.it ) and are plotted in Figs. 3a to 3c. As observed for other intramontane basins [Gubbio: Bindi et al. (2009); Norcia: Bindi et al. (2011)] there is a remarkable amplification of the ground motion in the centre of the basin, when compared to the rock outcrop, in terms of amplitude ground motion peaks (Tab. 1). In particular, Station SULA has recorded velocity and displacement peaks that are about 6 times the peaks recorded at the rock site SUL. Surface waves, that could be locally generated, are also observed in the records. The characteristics of the ground motion recorded at the stations in the basin are hints for a 2D or 3D amplification effects, that should be evaluated after a monitoring of the plain with a seismometric array. Tab. 1 - Peak ground acceleration, velocity and displacement (in bold the ratio between the peak values of soil sites, SULA and SULC, and the rock site (SUL) Station PGA (cm/s2) PGV (cm/s) PGD (cm) SUL 2.342 0.093 0.015 SULA 8.271 (3.53) 0.540 (5.80) 0.093 (6.20) SULC 4.927 (2.10) 0.363 (3.90) 0.062 (4.13) GNGTS 2014 S essione 2.2 265