Experts say it is too soon to know if the tectonic upheaval that shook northeast Japan last week has put Tokyo at greater risk.
Japan is still haunted by the "Big One" that devastated its capital in 1923 and left more than 140,000 dead, and the 1995 Kobe quake, which claimed 6400 lives.
But there area suggestions that the recent quake off the east coast of Japan could alter the odds of a 'megaquake' hitting the capital.
"That is going to be hotly debated in the scientific community," says Jochen Woessner, a seismologist with the Swiss Seismological Service in Zurich.
"There will very likely be a strong interaction with the Kanto Plains," says John McCloskey, a professor of Geophysics at the University of Ulster in Northern Ireland, referring to the seaside basin that holds greater Tokyo.
An earthquake doesn't always relieve stress - sometimes it redistributes it, says McCloskey.
"Places that have not failed during a quake can actually be more stressed by the earthquake happening beside them," he says. "But we can't tell at this stage whether it has made the next earthquake more or less likely."
For Jerome Vergne, a seismologist at Strasbourg University in eastern France, "the risk for Tokyo cannot have diminished."
Only in the region north of the quake's epicentre - some 400 kilometres northeast of Tokyo - would stress levels have relaxed, he says.
"An increase in loading" - added pressure - "could advance the date of a future quake near Tokyo," he says.
Tokyo's precarious placement
The Japanese capital is only 300 kilometres from an underwater "triple junction" where three of the two dozen tectonic plates that comprise Earth's constantly shifting crust meet.
Tokyo sits atop the Eurasian plate. Beneath it, the Philippine Sea plate descends, or subducts, from the south, while the Pacific plate slips down from the east.
Subduction is not a slow-and-steady process, but occurs in a "stick-slip" motion that gives rise to infrequent, but massive, convulsions.
A major earthquake in or near Tokyo could cause a trillion dollars in damage, experts have calculated.
Over the last decade scientists have developed computer programmes to measure stresses in Earth's outer layer in three dimensions, making it possible to see how those stresses might impact neighbouring faults.
But it will be several days, perhaps weeks, before we know whether the tectonic time bomb sitting under Tokyo may have been reset, says Bob Holdsworth, a professor of structural geology at Durham University in Britain.
"When you have a big event on one fault, it affects the behaviour of adjacent faults," he says. "The faults are, as it were, able to communicate with one another."
Patterns in aftershocks
McCloskey says last Friday's quake was, strictly speaking, an aftershock of a nearby 7.2 magnitude quake two days earlier, despite its far greater power.
"We have calculated that the stress field from the 7.2 quake on Wednesday is consistent with the triggering of this earthquake," he says.
But connecting the dots with the Tokyo region, several hundred kilometres distant, is far more difficult, he added.
Experts also look for patterns in the thousands of quakes that occur across the globe each year.
"Earthquakes are known to cluster, both is space and in time," says Holdsworth, pointing to recent quakes over 8.0 in or near Peru, Indonesia, China and Chile.
"There was a similar cluster spanning the period 1957-64, which included - around the Ring of Fire - the three biggest earthquakes on record," he says.
The Ring of Fire reaches from New Zealand to the coast of Chile in a 40,000 kilometre arc of nearly daily seismic violence around the Pacific rim.