Grünthal, Gottfried European Macroseismic Scale EMS-98, External Organizations;
http://www.gfz-potsdam.de/portal/gfz/Struktur/Departments/Department+2/sec26/projects/04_seismic_vulnerability_scales_risk/EMS-98/EMS-98_language_versions (Supplementary material)
http://bg.wikipedia.org/wiki/%D0%95%D0%B2%D1%80%D0%BE%D0%BF%D0%B5%D0%B9%D1%81%D0%BA%D0%B0_%D0%BC%D0%B0%D0%BA%D1%80%D0%BE%D1%81%D0%B5%D0%B8%D0%B7%D0%BC%D0%B8%D1%87%D0%BD%D0%B0_%D1%81%D0%BA%D0%B0%D0%BB%D0%B0 (Abstract)
Grünthal, G. (Ed.)(1998): Short form of the EMS-98 in Bulgarian, (Cahiers du Centre Européen de Géodynamique et de Séismologie ; 15), Luxembourg : Centre Européen de Géodynamique et de Séismologie.
