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Zidbits – Learn something new everyday! | November 1, 2014

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Can an earthquake shift the Earth’s axis?

Can an earthquake shift the Earth’s axis?

Several media sources have reported that the Chilean earthquake of 2010 and the 2011 Tohoku earthquake in Japan were so powerful, that they caused a shift or tilt in Earth’s axis. They claim that the earth, which is spins like a top as it orbits the sun, had its tilt permanently altered. It’s a pretty mind bending concept to think about – is there any truth to it?

The Simple Answer

The short & simple answer is yes. The earthquake that unleashed the devastating tsunami on March 11th, 2011 moved the entire main island of Japan by 8 feet (2.4 meters). It also shifted the Earth on its axis by nearly 4 inches (10 centimeters).

Scientists who are familiar with the phenomena say that the axis being altered has led to the shortening of the day by 1.8 microseconds, or just over a millionth of a second.

The Complex Answer

The complex answer is “maybe“. That’s because it depends on how you approach the question. The angular momentum of the Earth doesn’t change, but the angular velocity vector does. This is directly due to a shift in a body’s moment of inertia tensor. If you’re not familiar with physics, this all can be quite confusing.

TsunamiIn simpler terms; Earthquakes can’t change the axis of rotation, relative to a given inertial reference frame. That is, the axis of rotation doesn’t change relative to other stars as a result of an earthquake. If you were watching everything unfold from the comforts of an extrasolar planet, you wouldn’t notice a change in earth’s orbit or rotation.

However, because an earthquake moves the material around within the Earth itself, the position of the rotation axis relative to a marker or point on Earth’s surface changes. A close analogy would be to imagine a balloon that was filled with water and then thrown at a target. The balloon itself won’t spin or rotate very much, or not at all, but the water inside it will be slosh around. This ‘sloshing’ of the Earth’s mantle is what caused the crust to be shifted.

Rather than saying the earthquake shifted the Earth’s axis, it would be more accurate to say that it shifted all of the stuff on the Earth’s surface. Because we find it convenient to use points of reference that are on Earth’s surface, to us, it looks like a shift in the axis of Earth.

Our thoughts, prayers and support go out to the people of Japan during this tragic time. Stay strong Japan. If you would like to donate to the relief efforts, please visit the Red Cross website.

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