TOKYO (AP) — Japan was rattled by a strong aftershock and tsunami warning Thursday nearly a month after a devastating earthquake and tsunami flattened the northeastern coast.The Japan meteorological agency issued a tsunami warning for a wave of up to 6 feet. The warning was issued for a coastal area already torn apart by last month's tsunami, which is believed to have killed some 25,000 people and has sparked an ongoing crisis at a nuclear power plant.Officials say Thursday's aftershock was a 7.4-magnitude and hit 25 miles under the water and off the coast of Miyagi prefecture. The quake that preceded last month's tsunami was a 9.0-magnitude.Buildings as far away as Tokyo shook for about a minute.In Ichinoseki, inland from Japan's eastern coast, buildings shook violently, knocking items from shelves and toppling furniture, but there was no heavy damage to the buildings themselves.