Basement 13 : Harder and usually older igneous and metamorphic rocks that underlie the main sedimentary rock sequences (softer and usually younger) of a region and extend downward to the base of the crust
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}