The initial 9.0-magnitude earthquake at 2.46 p.m. local time (0546 GMT) was centered about 130 kilometers (80 miles) east of Sendai in Japan, on the nation's main island of Honshu. It struck about 24.4 kilometers (15.2 miles) deep, according to the Japan Meteorological Agency (JMA).
On Sunday, JMA said that based on the occurrence of aftershocks so far, there is a 70 percent chance that an aftershock of 7.0 on greater will hit by 10 a.m. local time on Wednesday. After Wednesday morning, the chance of such an earthquake happening will be about 50 percent until 10 a.m. local time on Saturday.
"Tsunami may occur after a strong aftershock. Be cautious when a tsunami warning or advisory is issued," the seismological agency said in a statement. "The area is so large that, when compared to past cases, the activity of aftershocks is very high."
Japan has been rocked by dozens of strong aftershocks since Friday afternoon, but only one of them exceeded magnitude 7.0. The 9.0 monster quake unleashed a huge tsunami, devastating local coastlines and killing more than 1,000 people. Fears are the death toll will exceed 10,000.
