quake

The first was a magnitude 3.8 quake, which was followed a minute later by a magnitude 3.5 temblor, according to the U.S.

This combination of chemical and biological changes indicates that the quake swarm temporarily boosted the resources available to deep microbial life.

Before the 2011 quake and tsunami, which killed around 18,000 people, nuclear power generated about a third of Japan's electricity, with fossil fuels contributing most of the rest.

Scientists rate the strength of an earthquake using the moment magnitude scale, a system that gauges the amount of energy released by the quake and assigns it a number.

This shallowness means that such quakes can cause more noticeable and potentially damaging ground movement.