Why Tokyo Gets Bad Earthquakes

The ruins of the Ginza after the 1923 Great Kanto (Tokyo) Earthquake and fire. (Photo from Geography Department Hewett School)

What Is Giving Tokyo A Headache? -- IOL

Paris - A massive slab of rock lurking beneath the Kanto Plain on the central Japanese island of Honshu is a major source of the earthquake threat that dogs Tokyo, scientists said on Sunday.

Around 100 kilometres wide and 25km thick, the chunk is jammed between tectonic plates that converge beneath the flat, densely-populated plain.

The giant fragment is a potent trigger for a hugely destructive kind of quake, for it wedges between two of the plates and prevents them from sliding smoothly over one other.

As a result, tensions build up until the stored energy is released catastrophically, rather than in smaller, safer movements, the experts say.

Tokyo is built atop the Eurasian plate, one of the two dozen or so tectonic plates that, like jostling pieces on a jigsaw puzzle, comprise earth's surface.

Around 100km to the northwest of the city, on the Kanto Plain, the local geology becomes complex, turning into a triple-layer subterranean sandwich.

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