Influence of observation floor and building height on macroseismic intensity

Abstract

The perception of an earthquake depends on whether the observer is located on a lower or upper floor within a building. Macroseismic scales propose only a qualitative description of the varying effects felt that are dependent on the floor the observer is on. To quantify these effects, in this study, we analyze 45,000 macroseismic questionnaires collected in Italy reporting on transitory effects. The questionnaires pertain to buildings no more than 10 stories high and are derived from municipalities experiencing a Mercalli-Cancani-Sieberg (MCS) intensity less than or equal to VII with the majority being III and IV. We find that the intensity variation caused by the increased shaking on upper floors can be quantified. The upper floor intensity increases by 0.4 MCS compared with ground and underground levels. After correcting for an average floor-dependence factor, we find a further building height effect evident in short buildings that are probably exposed to less intense shaking. This effect displays a variation with the hypocentral distance reaching an MCS intensity of -0.3 at distances on the order of 200 km.