Japan earthquake: Fukushima nuclear plant remains the gap in a wall of disaster defences

Japan earthquake: Fukushima nuclear plant remains the gap in a wall of disaster defences

Japan earthquake: Fukushima nuclear plant remains the gap in a wall of disaster defences

Updated 22 November 2016, 18:05 AEDT

Japan has the most sophisticated earthquake detection network in the world, but warnings are only effective if people heed them, writes Mark Willacy.

Disasters and Accidents:Earthquake:ALLDisasters and Accidents:ALL:ALLDisasters and Accidents:Nuclear Accident:ALLEnvironment:Nuclear Issues:ALLJapan:ALL:ALLfukushima, earthquake, japan, aneyoshi, tsunami, mark willacy, nuclear plantABCBy Mark WillacyJapan earthquake: Fukushima nuclear plant remains the gap in a wall of disaster defencesJapan has the most sophisticated earthquake detection network in the world, but warnings are only effective if people heed them, writes Mark Willacy.

They appear as biblical stone tablets, promising salvation to those who heed their commandments.

Many of these tsunami stones are hundreds of years old, and they dot the seismically volatile north-east coastline of Japan's main island of Honshu.

After the 2011 tsunami I visited the tiny village of Aneyoshi, a smattering of 11 homes on an isolated peninsula.

It had been wiped out by massive waves after offshore earthquakes in 1896 and 1933, so the survivors had retreated up into the mountains, rebuilding their homes and carving a warning into a stone tablet erected just below the village: "Do not build your homes below this point!"

Aneyoshi was one of the few communities on this stretch of the coast that was untouched by the massive tsunami of 2011.

They had listened to the warnings of their ancestors, and they had survived.

These days, cell phones have replaced stone tablets as Japan's early warning system.

Japan has the most sophisticated earthquake detection network in the world — a system of 4,235 seismometers can detect the very first waves from a quake, before estimating its focus, magnitude and seismic intensity.

Phone alerts are then sent out, giving people precious seconds to prepare themselves for the shaking to come.

In the wake of the magnitude-9 earthquake of March 2011, which spawned a tsunami that killed more than 18,000 people, the Japanese pay special attention to these phone alerts.

The earthquake today off Fukushima underlines how important these early warning systems are, in a country that has more large earthquakes than any other, and from where the word "tsunami" — meaning harbour wave — originates.

But like the tsunami stones that dot the Japanese coast, warnings are only effective if people heed them.

Today's earthquake and tsunami has again exposed one gap in Japan's wall of disaster defences — the Fukushima Dai-ichi nuclear plant.

Every time there is a sizeable tremor off that stretch of coast all eyes immediately turn to this sprawling facility, where three reactors melted down after being swamped by the 2011 tsunami.

While the reactors are under control, a constant stream of water has to be pumped over the melted blobs of nuclear fuel to keep them cool.

According to the plant operators, TEPCO, today's quake caused no serious damage to the site, which will take at least 40 years to clean up and decommission.

But 12 kilometres further down the coast, its sister plant, Fukushima Dai-ni, did experience something of a safety hiccup.

Dai-ni was also hit by the 2011 tsunami, but managed to shut down without triggering a meltdown.

Today, however, the cooling system for one of the plant's spent fuel pools stopped — and while there was no immediate danger, it did take 90 minutes to fix it.

Today's earthquake rattled nerves and, again, exposed the ongoing challenges of making the reactors of Fukushima safe.

It also reminded the Japanese that warnings — whether they be inscribed in stone, or sounding from cell phones — should never be ignored.

Mark Willacy was the ABC's Tokyo correspondent between 2008 and 2013, and he won a Walkley Award for his coverage of Japan's 2011 tsunami and Fukushima meltdowns. ABC TV will air his documentary, Fukushima, at 9:30pm on December 19.

internationalTsunami inspectionPeople keep a lookout for tsunami waves in Japan's Fukushima prefecture.