TOKYO: A strong undersea earthquake with a magnitude of 6.4 struck southeast of Tokyo on Friday morning, the U.S. Geological Survey (USGS) said. There was no tsunami warning issued by the Pacific Tsunami Warning Center in Hawaii.Japan’s weather agency said there could be slight changes in the sea level but no damage to Japan. The quake’s epicenter was 226 kms (138 miles) southeast of the Japanese capital at a shallow depth of 10 km (6 miles), the USGS said.