On the one-month anniversary of the worst natural disaster to ever hit Japan, yet another magnitude 7.1 earthquake has hit northeast Japan prompting the government to issue a tsunami warning, although theheight of the waves are estimated to be no more than 50cm.

According to reports, the ground was shaking up and down as well side to side, as the earthquake hit on Monday. It is unclear if the latest earthquake has caused further damage to the Daiichi nuclear plant in Fukoshima, although workers there have been temporaritly evacuated.

It’s been a month since a magnitude 9.0 quake hit Japan’s northeast region, sending a roiling tsunami – a tower of waves measuring as high as 23 m in some areas – crashing into coastal towns and killing thousands of people.

[From Japan marks one month since quake – Asia-Pacific – Al Jazeera English]

This one was much closer, much shallower, on land and felt very much stronger than the other 7.1 that struck on Saturday night. That one was 40km underwater. Electricity to the Fukushima reactors has been lost and the cooling water pumps are down.