According to Japan's Meteorological Agency, earthquake hit about 750 km northeast of Tokyo and 30 km below the sea surface. However, the tremor was not felt in Tokyo.
The two tremors are believed to be unrelated and did not affect the crippled Fukushima Daiichi plant or other nuclear plants in the region.
The March 11 9.0 magnitude earthquake and tsunami had wiped out large parts of Japan"s northeastern coast leaving nearly 20,000 people dead or missing. The twin disasters also triggered a nuclear crisis, forcing about 100,000 people to flee their homes due to leaking radiation.