The day the Earth heaved

Date:1 July 2011 Tags:, ,

The colossal 9.0 earthquake in Japan shifted enough mass to make Earth rotate faster. Richard Gross, a geodynamics scientist at Nasa’s Jet Propulsion Laboratory, compares the phenomenon to a spinning ice skater. “She moves her arms closer to her body, moving her mass closer to the axis about which she’s rotating,” he says. “Earthquakes do the same thing.” The stronger the quake, the greater the Earth’s deformation and its effect on rotation.

Gross calculated a 17 cm shift in the axis around which Earth’s mass is balanced – twice that caused by the quakes under the Indian Ocean in 2004 and in Chile in 2010. Although the consequences of such a shift are mostly negligible, it can affect spacecraft navigation. Even a tiny change in the angle at which a spacecraft leaves Earth could mean a large guidance problem across tens of millions of kilometres. – Andrew Moseman

How earthquakes affect time

1 The north–south axis runs through the poles.

2 The Earth’s mass balances around its fi gure axis, which is about 10 m off from the north-south axis.

3 The March 2011 Japanese quake shifted the Earth’s figure axis by 17 cm.

Disaster by the numbers

Distance Honshu moved east after the quake

The Pacific continental plate is sliding beneath the North American plate, causing tension. When this pressure was released in March, the land surged upward and east, causing a massive earthquake and shifting the location of Honshu. – Alyson Sheppard

32 km
Depth of earthquake

During the quake, the ocean floor jutted up about 40 m and slipped over an area about 300 km long and 145 km wide. This thrust the water column upward, generating one tsunami that travelled east to California and another that headed west to Japan.

800 km/h
Velocity of tsunami

In the open ocean, the tsunami wave nearly reached the speed of a commercial jet airliner. The wave slowed as it approached the coast, but the slope of the continental shelf boosted the wave’s maximum height to nearly 37 metres.