A strong earthquake rippled through the Hawaiian Islands, shaking residents and tourists from their sleep, knocking out electrical power to several areas and triggering a landslide that rained boulders and other debris on the major highway of the largest island. The U.S. Geological Survey said that the main earthquake Sunday had a preliminary magnitude of 6.6 and that there had been at least a dozen aftershocks, including one that measured 5.8. Officials rated the quake as the largest to hit Hawaii since a magnitude 6.7 quake struck in 1983.