As far back as 373 BC people have claimed to see weird lights in the sky during earthquakes, and sometimes for minutes before the shaking actually starts, as seen in this video:
They seem to occur in China quite often, probably because the government only permits people to see a rainbow if they are moments from cataclysmic natural destruction. The lights were also witnessed during the recent earthquakes in Peru.
So, What Do the Smart People Think is Happening?
There are a number of theories surrounding earthquake lights, but unfortunately none of them are very conclusive. One suggests that the imminent earthquake releases gases that are electrically charged in the air, while another says that the tectonic stress fucks with the magnetic field of the earth and creates an aurora.
Yet another claims that the ground beneath contains a lot of quartz, which sparks up like Blanka from Street Fighter 2 when shaken by a tremor. Not one of these theories has a shred of evidence to back it up, though, so really we would accept any theory as long as we can tie it to some kind of fighting game reference.