Comparison of damage data from questionnaires and field survey: the case of the June 20, 1978 Thessaloniki (northern Greece) M6.5 earthquake

The earthquake of June 20, 1978 (M6.5) near Thessaloniki, Greece, and the abundant information on damage distribution provided researchers with an opportunity for a more detailed study of earthquake effects. The damage on buildings caused by that earthquake was recorded in several ways. In this paper two of them will be presented and discussed: First, the use of questionnaires filled in by citizens and second, the in situ inspection of the buildings by a team of expert engineers, enriched by data of retrofitting costs, where available. In the current study, the damage data derived from the questionnaires are compared against the ones given by the engineers after they have been both converted to the European Macroseismic Scale 1998 (EMS-98) Damage Grades. It is observed that for EMS-98 damage grades equal and larger than 2 the questionnaire method overestimates damage while for lower grades both approaches provide comparable results.