Inspired by the urban legend that if all the people in China jumped at once it would alter the orbit of the Earth, German scientists (working in participation with a German TV show)
staged an experiment at a music festival. They arranged for all 50,000 people at the concert to jump at once, and then measured the results. They called it a "gang boing." Here's what happened:
In the end, the hoppers created "a mini-mini-earthquake," according to Ulrich Grünewald, who produced the segment for a science program on German television. The ground moved one-twentieth of a millimeter, with four oscillations per second. Scientists from Germany’s Geological Research Institute measured movement up to a kilometer away...
"We showed that people cannot start a (real) earthquake by hopping," Grünewald told the dpa news service. An actual earthquake would contain billions of times more energy than the jumping Germans produced.
Comments
In 1988, during an LSU vs. Auburn (then #4 in the nation) football game in Baton Rouge, a last minute touchdown gave LSU the win. The crowd reaction to that TD registered on the seismographs on campus. It's been known as the "Earthquake Game" ever since.
BTW, the stadium at that time held over 80,000.
http://www.lsu.edu/highlights/033/football.html