Miti e leggende intorno allo tsunami

Yahoo! News - Sumatran Quake Left 'Scar' on Earth's Gravity: "The magnitude 9.3 earthquake has already been said to have shortened the day by fractions of a second, shifted the North Pole by an inch, and made the planet less fat around the middle.

The new prediction comes from Roberto Sabadini and Giorgio Dalla Via at the University of Milan. The idea is fairly straightforward. The strength of Earth's gravity varies depending on the depth of a trench or height of a mountain, as well as the density of material. Even changing tides alter the gravity field.

The Dec. 26, 2004 quake lifted an 18-foot (6 meter) ledge along a 620-mile (1,000 kilometer) fault.

Gravity variations are measured using the geoid, which is similar to sea-level. The geoid is a hypothetical 'surface' around the Earth at which the planet's gravitational pull is the same everywhere. Over dense areas, the geoid moves away from the real surface, and where gravity is less, the geoid moves closer to the real surface.

[In] The Sumatran quake, the geoid moved as much as 0.7 inches (18 millimeters), the scientists predict."