Frequency 21 : General. The number of times something happens in a certain period of time, such as the ground shaking up and down or back and forth during an earthquake
Natural and Environmental Disaster Information Exchange System NEDIES, European Commission, Directorate General Joint Research Centre (DG JRC), Institute for the Protection and Security of the Citizen (IPSC), Ispra (Varese) Italy, http://nedies.jrc.it/index.asp?ID=82#Top, ScienceMaster, physical Science, Earthquake Glossary, CA, USA 2010. http://www.sciencemaster.com/physical/item/earthqu ake_glossary.php, (ND/ Erthq - Amer) {161}