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3D Ground-Motion Estimation in Rome, Italy

¹ Department of Geological Sciences
5500 Campanile Drive
San Diego State University
San Diego, California 92182-1020
 (K.B.O.)

² Istituto Nazionale di Geofisica e Vulcanologia
Via di Vigna Murata
605 00143 Rome, Italy
 (A.A., A.R., F.M., L.M.)

View larger version (69K): [in this window] [in a new window]   Figure 1. The seismicity near Rome estimated from earthquakes of the Italian catalog, Catalogo Parametrico dei Terremoti Italiani (Gruppo di Lavoro, CPTI, 1999). Dotted rectangles present the two main seismogenic districts affecting the city (the Central Apennines and the Alban Hills). We simulate ground motions produced in the city by two scenario earthquake locations: (1) the Alban Hills, at an average distance of 25 km from Rome and (2) the Central Apennines located 80–100 km from Rome. The filled star shows the epicenter location of the M 5.3 Alban Hills scenario earthquake. Solid rectangles depict the Rome model and the fault projection that is used for the Central Apennines scenario earthquake, taken from the database of Valensise and Pantosti, (2001) for the 13 January 1915 Fucino earthquake, M 7.0. The horizontal line depicts the profile used to display synthetic seismograms for the Fucino earthquake scenario in Figure 9.

View larger version (69K): [in this window] [in a new window]   Figure 2. Lithologic map of the urban area of Rome together with the distribution of the damage caused by the 1915 Fucino earthquake (after Ambrosini et al., 1986). Three types of damage are distinguished: slight damage (cracking of plaster, the downfall of small pieces of moldings), intermediate damage (between slight and heavy damage), and heavy damage (deep and diffuse damage of indoor and outdoor walls, downfall of large parts of moldings and of chimneys).

View larger version (34K): [in this window] [in a new window]   Figure 3. Lithological interfaces used to generate the 3D velocity model below Rome. (top) Depth to bottom of the alluvium. (middle) Depth to bottom of the Pleistocene. (bottom) Depth to bottom of the Pliocene.

View larger version (31K): [in this window] [in a new window]   Figure 4. Regional 1D velocity and density model used in our scenario simulations.

View larger version (90K): [in this window] [in a new window]   Figure 5. Six-time-window slip distribution used for the M 7.0 Central Apennine earthquake scenario. Two slip distributions are used: (1) shown above and (2) a lateral mirror image of (1).

View larger version (78K): [in this window] [in a new window]   Figure 6. Snapshots of wave propagation for the M 5.3 Alban Hills scenario in Rome. The snapshots depict particle velocities at 10-sec intervals after the origin time of the earthquake. The thick line shown on the snapshots is the 50-m-depth contour of the isosurface of Vs = 250 m/sec and depicts the outline of the valley. The particle motion is scaled by the same constant for all snapshots.

View larger version (72K): [in this window] [in a new window]   Figure 7. (top) Maps of maximum peak velocities in the Tiber River valley for the M 5.3 Alban Hills scenario, superimposed with the 50-m-depth contours for the isosurface of Vs = 250 m/sec. The peak velocities are scaled by the same constant for all components. The triangles indicate the location of Prati (Pra), Colosseum (Col), and Vatican City (Vat). The dashed line depicts the profile used to display synthetic seismograms (bottom).

View larger version (44K): [in this window] [in a new window]   Figure 8. 3D synthetic velocities (top) and accelerations (bottom) for the Alban Hills scenario at selected locations in Rome (see Fig. 7).

View larger version (121K): [in this window] [in a new window]   Figure 9. East–west component seismograms along an east–west profile from the fault to Rome for the M 7.0 Apennine scenario earthquake, for six different realizations of the source process (hypocentral location toward the northwest, center, and southeast of the fault, and slip distributions 1 and 2, see Fig. 5) and their east–west peak velocities (bottom). The top panel shows the east–west seismograms for a simulation with an elastic (loss-less) regional model and hypocenter location in the center of the fault and slip distribution 1.

View larger version (67K): [in this window] [in a new window]   Figure 10. 0–1 Hz peak velocities in Rome, relative to the value in rock, for a vertically incident planar SH wave.