RESONANCE OF SUBSURFACE SEDIMENTS - AN UNFORESEEN COMPLICATION FOR DESIGNERS OF ROMAN COLUMNS

Most of ancient Rome was settled on the Tiber River Holocene flood pla in. Monuments of Imperial age (I to V century) show evidence of signif icant damage, mainly produced by earthquakes generated in the seismoge nic areas of the Central Apennines, 70 to 130 km away from Rome. The d ifferent level of damage suffered by the two most important honorary c olumns in Rome, those of Trajan and Marcus Aurelius, located 700 m apa rt, suggests the occurrence of strong variations of ground motion acro ss a narrow zone due to changes in the local geology. In order to chec k this hypothesis, we investigate the details of surface and subsurfac e geology of the area. We construct a 2D geological profile which incl udes topographic variations and heterogeneities of the elastic and ane lastic parameters. A finite-difference technique is used to compute th e SH-wave response along the profile. Numerical modeling of seismic re sponse at the site of Marcus Aurelius' column shows a significant spec tral amplification in a narrow frequency band corresponding to the nat ural vibrational mode of the column, The amplification attains much lo wer values at the Trajan's column site.