Tsunami-Triggering-Earthquake Shook Entire Planet

Iphtashu Fitz writes "The earthquake that triggered last years tsunami was the largest one recorded in 40 years and kept the planet shaking for weeks according to new reports that are due to be released on Friday. This was the largest earthquake measured so far by a new worldwide array of digital seismic instruments, whose results will appear in six different reports being published in the journal Science tomorrow. The quake broke several records, including the longest fault line (720 to 780 miles) and longest duration (10 minutes). The water displaced by the rise of the sea floor in the quake zone also resulted in a rise of worldwide sea levels of 0.004 inch. In Sri Lanka, more than 1,000 miles from the epicenter, the ground moved nearly 4 inches. As many as 14 smaller quakes were triggered in Alaska when the tremors from this quake reached the northernmost U.S. state."

Comments

It's just a matter of *time*

[helioquake]

Well well, just imagine a chunk of water floating inside a space station. Initially it'd be more or less spherical at rest. But once an astronaut pokes on it, it starts vibrating in many different modes...but its vibration eventually dies down, thanks to the air molecules surrounding the water bubble.

Basically the same thing is happening to the Earth. But in this case, the air (atmosphere) is thinner and there is nothing outisde (vacuum). So dumping the vibration energy takes time. Eventually the energy would turn into heat via friction, however.

Re:It's just a matter of *time*

[osmic234]

Well well, just imagine a chunk of water floating inside a space station. Initially it'd be more or less spherical at rest. But once an astronaut pokes on it, it starts vibrating in many different modes...but its vibration eventually dies down, thanks to the air molecules surrounding the water bubble.

Basically the same thing is happening to the Earth. But in this case, the air (atmosphere) is thinner and there is nothing outisde (vacuum). So dumping the vibration energy takes time. Eventually the energy would turn into heat via friction, however.

This is a nice analogy, but it's not the air molecules surrounding the water bubble that are the dominant factor in attenutating the vibrations, but rather the internal dissaption of kinetic energy to heat through friction. A lump of water floating in a vacuum would still come to rest, but just very slightly slower.

These vibrations are called spherical harmonics, and are often compared to a bell ringing - it's only larger earthquakes with sufficient energy that produce observable normal and tesseral (I think - been a few years since I've done this) modes. These describe in-and-out, and up-and-down patterns of vibrations respectively.The great 1960 Chilean earthquake (biggest earthquake of the last 100 years) was the first earthquake large enough to produce spherical harmonics that could be seen with m a global seismometer network.

Spherical harmonic oscillations (the in-and-out normal modes) have also been observed on the surface of the Sun - leading to a branch of science called Helioseismology. As in the earth, analysis of these vibrations provides further constraints on the internal structure.

A few people have suggested that there are interactions between the atmosphere and the earth. One published theory said that the atmosphere could actually drive spherical harmonics, which is pretty much opposite to what you'd think intuitively. I seem to remember that this theory was shot down though.