Japan: Another Earthquake

A 7.1 magnitude earthquake rattled Tokyo over a minute on Thursday night. Weaker than the M 9.0 that struck on March11, the 7.1 scared many people.

A warning of a tsunami of up to 6 feet was issued by the Japanese meteorological agency after a M7.1 shake off the coast, 60 miles from Sendai and 90 miles from the crippled and leaking nuclear power plant at Fukushima. Tokyo, which felt the earthquake, is about 215 miles from the epicenter. The tsunami warning was lifted after 90 minutes. The earthquake occurred at 23.32 local time. At first the quake was reported at M7.4, later downgraded to 7.1.

This latest strong aftershock has knocked out power in several areas in the Northeast and may have further damaged the Fukushima plant. Workers have evacuated the plant until the danger of a tsunami generated by this latest shock is past.

Plates warped and strained

This earthquake was 25 miles deep and is thought to be an aftershock or a continuation of the pressure release from the warping of the tectonic plates as the Pacific plate slides under Japan. Thomas Heaton, California Institute of Technology geophysicist, said after the March 11 earthquake that even one of magnitude 9 may not release the strain.

Japan mostly lies on the Okhotsk Plate, which is long and moving in a southerly direction. On the west side of Japan is the Eurasian Plate, pushing eastwards, and on the opposite side is the Pacific Plate, moving to the west. The Okhotsk Plate is therefore sandwiched between the two massive plates and being assaulted from both sides.