TOKYO (AP) - A strong earthquake has shaken northern Japan, and regional tsunami advisories have been issued. The Japan Meteorological Agency said Wednesday evening's earthquake was 6.8 preliminary magnitude off the coast. A tsunami of about a half-meter was expected for Aomori and Iwate prefectures. Iwate was in the region heavily damaged by last year's earthquake and tsunami. The epicenter was about 146 miles (235 kilometers) south of Kushiro, Japan, on Hokkaido, Japan's northern island. It was a relatively shallow 16 miles (26 kilometers) from the ocean floor. The Pacific Tsunami Warning Center in Hawaii said there was no threat there or across the Pacific.