TOKYO—Federal Reserve Chairman Alan Greenspan described himself as "shaken but all right" Monday following an incident in which several thousand excited young Japanese fans mobbed and tipped over his tour bus after a speech at the Tokyo Dome. "Mr. Greenspan is at the height of his popularity in Japan right now," said Martine Engers, a publicist for the chairman, who is currently in the midst of a 41-city world tour. "And I guess we simply weren't prepared for this level of fan hysteria." Before military police restored order, thousands of frantically speculating youths drove the Nikkei average past 16,000.