Moon Shake

By the term Moon-shake I was actually referring to moonquake. When moonquake occurs it rings like a bell . You may think that if moon rings like a bell then it must be hollow inside. But it isn’t!. You may also ask that why don’t we hear the ringing sound.

When there's an earthquake, vibrations travel through rock, just as they do through a bell to create a ringing sound. We know our planet rings like this because of seismometers (instruments that measure the vibrations of the Earth moving beneath our feet). We don't hear the Earth ringing because these rock vibrations, called seismic waves, have a frequency spectrum below 1 hertz. The lowest frequency human ears typically can hear is 20 hertz. By speeding up seismic waves hundreds or even thousands of times, you can hear what an earthquake sounds like.

 It's not just the Earth that rings when the ground is disturbed; the Moon also rings.

Astronauts put seismometers on the Moon during the Apollo missions in the 1960s and 70s.Rather than wait around for a moonquake or for a meteor to hit the Moon, astronauts set off small explosives to create seismic waves but those couldn’t create enough vibrations. To create bigger vibrations, they needed a bigger bomb. On the Apollo 12 mission, after they'd left the surface of the Moon and returned to the command module, orbiting above, they sent their lunar module back down to the Moon's surface. It hit the ground with the force of 1 ton of TNT. As recorded by the seismometer, the shockwave lasted for an hour.

Again, on the Apollo 13 mission astronauts, they dropped their S-IVB, one of the stages of their rocket, and it hit the Moon with the force of 11.5 tons of TNT, and the shockwaves lasted nearly three and half hours.

 

There are 4 types of moonquake.

(1)Deep moonquakes about 700 km below the surface, probably caused by tides;

(2) Vibrations from the impact of meteorites;

(3) Thermal quakes caused by the expansion of the frigid crust when first illuminated by         the morning sun after two weeks of deep-freeze lunar night; and

(4) Shallow moonquakes only 20 or 30 kilometers below the surface.

The first three are mild and harmless but shallow moonquakes last quite long.

Now the question is: why the duration of earthquake is so short and the duration of moonquake is so long?

Well, the reason has to do with chemical weathering. Water weakens stone, expanding the structure of different minerals. When vibrations propagates across such a compressible structure, it acts like a foam sponge as a result it deadens the vibration.

On the other hand, the Moon is very dry, cool and mostly rigid, like a chunk of stone or iron. So moonquakes set it vibrating like a tuning fork. Even if a moonquake isn’t intense it just keep going. Some people may say that the moon is hollow that’s why it vibrates so long like a bell or tuning fork. Well, there is a hypothesis called The Hollow Moon hypothesis or Spaceship Moon hypothesis which proposes that Earth's Moon is either wholly hollow or otherwise contains a substantial interior space but no scientific evidence whatsoever exists to support the idea;