Probably, but this quake was somewhat bigger at 9, and it seems to have been caused by a Splay - a newly appearing tectonic fracture which hadn't been known about, the same sort of scenario as posed in the film, 2012.
It's a massive domino effect, it seems; the reactors have all been shut down, but the heat inside is taking a long time to escape and the pressure inside is resisting their attempts to get coolant in. Briefly, although all four reactors automatically shut down immediately after Friday's earthquake, engineers have struggled to cool down the reactor cores, because pumps that should have driven cooling water into the reactors failed. This meant that the reactors overheated, turning the water into steam.
The engineers therefore vented the steam, carrying some radioactive caesium-137 and iodine-131 (both of which are produced by the uranium in the fuel rods) into the environment. The fuel rods are tubes of zircoloid stuffed with uranium dioxide. When these aren't cooled enough, they swell up and can crack. At that point, radioactive caesium and iodine gases can escape. As the zircoloid heats up, it reacts with the cooling water to form hydrogen, which is a highly explosive gas. This was to blame for the dramatic explosions that damaged the outer buildings of reactors 1 and 3.
However, it is now reactor 2 that is causing the most concern. Replacement pumps intended to inject cooling water have repeatedly failed, meaning that water levels fell and the fuel rods overheated still further. According to Kyodo News:
Water levels sharply fell and the fuel rods were fully exposed for about 140 minutes in the evening as a fire pump to pour cooling seawater into the reactor ran out of fuel and it took time for workers to release steam from the reactor to lower its pressure, the government's nuclear safety agency said.
Then within the last few hours a further accident occurred. Kyodo News reports:
Tokyo Electric Power Co. said Monday fuel rods were fully exposed again in the No. 2 reactor of the Fukushima No. 1 nuclear power plant as of 11 p.m. TEPCO said a steam vent of the pressure container of the reactor that houses the rods was closed for some reason, leading to a sudden drop in water levels inside the reactor.
This series of coolant failures has increased the chance that the fuel rods will start to melt. If you fail to cool it, the uranium can melt and it will all fall to the bottom as a big soup.
But even if the rods do melt and sink to the base of the reactor vessel, this shouldn't be a problem unless the vessel itself breaks open.
"The big question is whether the containment holds," says Wakeford. "There was a meltdown at Three-Mile Island, but the vessel remained intact."
Wakeford says there is no chance of a "China syndrome" scenario, with the fuel burning its way right through to the earth's core with potential to blow up the planet.
The repeated coolant failures have made the situation much worse, because temperatures and pressures will have risen much more. The pressure vessel that contains the fuel rods will have some threshold beyond which it cannot cope, and will break open.
If the pressure vessel does burst, radioactive gases would be released, mainly caesium-137 and iodine-131. Radioactive iodine is the biggest problem, because if it contaminates drinking water or milk, it can be taken up by the thyroid gland, potentially leading to thyroid cancers as seen in the wake of Chernobyl.
Much more long-lived, with a half life of 30 years, is the other potentially dangerous element that could be released: caesium-137. This has been the most problematic legacy of Chernobyl, as it was carried throughout western Europe by the wind. Wakeford says that the Japanese authorities need to do whatever they can to prevent it escaping.
