It seems as if we are talking about a literal 700 tons of explosives, not explosive yield.
http://apnews.myway.com/article/20060331/D8GMGPLG8.html
"Plans for a Pentagon-led experiment that involves detonating 700 tons of explosives in the desert drew criticism from state leaders and a disarmament activist."
"The test, named "Divine Strake," will involve nearly 40 times the amount of commercial ammonium nitrate and fuel oil explosive set off in the largest open-air, non-nuclear blast at the site to date. In 2002, 18 tons of explosives were set off at the Nevada Test Site."