Powerful earthquake hits northern Japan

TOKYO - A powerful earthquake with a preliminary magnitude of 7.1 struck Japan's northern island of Hokkaido this morning, injuring at least 13 people, swaying buildings and triggering a small tsunami wave.

There were no immediate reports of damage following the 3:32 a.m. quake.

Japan's Meteorological Agency quickly issued a tsunami warning for the eastern shores of Hokkaido's Pacific coastal area. Tsunami are potentially dangerous waves triggered by seismic activity.

But agency official Masahiro Yamamoto later told a televised news conference that the agency had lifted its warning, saying it had detected a 4-inch tsunami and expected only small changes in the ocean's surface.

The quake was centered off Hokkaido's east coast, about 550 miles northwest of Tokyo, 30 miles below the sea surface. The rocking was felt throughout northern Japan, including Hokkaido's largest city, Sapporo, and Kushiro, on the island's eastern shore.

A 4.6-magnitude aftershock followed the initial tremor about a half hour later.

National broadcaster NHK showed footage of desks rumbling in their offices and convenience store goods thrown from shelves by the force of the quake.

Most of the injuries were in the cities of Kushiro, Nemuro and Bekkaicho.