Skyscrapers are designed to absorb the shock, so it will not collapse with an earthquake.
But if the intensity is 6 (in Japanese scale), the highest floor will rock slowly to and fro, for about 2 meters. Keep away from the windows, and hold on to fastened objects. For descriptions on the intensity, please see: http://www.kishou.go.jp/know/shindo/shindokai.html
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