For more information on computation, see the article Bossu et al., 2016:

• Thumbnail Based Questionnaires for the Rapid and Efficient Collection of Macroseismic Data from Global Earthquakes, Rémy Bossu, Matthieu Landès, Fréderic Roussel, Robert Steed, Gilles Mazet-Roux, Stacey S. Martin, and Susan Hough. Seismological Research Letter. Oct 2016. doi: 10.1785/0220160120;
• Furthermore, to avoid the association with wrong events, we filter testimonies in distance and in intensity depending on the magnitude of the seismic event.
• (*) The "Main city" in the table above is estimated using the cities1000 data from geonames.org. The "-" means that no city is found in this database.