What are Moonquakes?

There are billions of people living in earthquake-prone areas worldwide, and as history (and several Hollywood depictions) have proven, earthquakes may be devastating. These natural events are dangerous and unpredictable, from toppling skyscrapers to cracking apart the earth's surface. Our lovely moon, nearly 240,000 miles away from our planet, deals with a similar problem, although these are referred to as moonquakes. Moonquakes receive little attention because no one lives on our lunar neighbour, yet they can be compelling and last up to 20 times longer than earthquakes on Earth. These quakes could be a significant issue if humans ever decide to occupy our nearest celestial neighbour, so understanding them is critical.

How do we know Moonquakes Exist?

There are only a few types of earthquakes on our planet, yet the severity range might be broad. They are triggered by tectonic plate movement, usually when a massive chunk of rock breaks, releasing energy that has been building up over time. Due to the rubbing and friction of the plates as they readjust and re-settle, seismic waves are released along the fault line, the boundary between the enormous tectonic plates. Thousands of moonquakes have struck the moon's surface since the 1970s.

Since we haven't travelled to the moon since 1972, how do we know that moonquakes still occurred? On the Apollo 17 mission, astronauts left seismometers at numerous landing sites on the moon, detecting seismic activity on the lunar surface with high precision. These seismometers were only operational for five years, ending in 1977 due to budgetary constraints, yet during that time, they recorded almost 12,000 earthquakes! In comparison, Earth experiences roughly 20,000 earthquakes every year, but our planet is far larger, and many of those quakes are mild and go undetectable by humans; only sensitive instruments can detect them.

The Four types of Moonquakes

Like Earth, the Moon has its own types of earthquakes that differ from each other Deep moonquakes, shallow moonquakes, meteor impacts, and thermal moonquakes are the four types of moonquakes that occur on the moon.

Deep Moonquakes

Deep moonquakes are highly common, occurring almost 700 kilometres beneath the moon's surface over roughly 27 days. The tidal pull of Earth on the moon, according to most scientists, is to blame. Although the moon moves the tides in our oceans, the Earth dramatically affects the moon, literally splitting its deep rocky core.

Meteor Impacts

Meteor impacts can also cause moonquakes, and because the moon has no atmosphere, every tiny meteorite heading for it will strike it instead of burning up in the atmosphere as it does on Earth. These collisions result in rippling earthquakes that seismometers can detect.

Thermal Moonquakes

Thermal Moonquakes are the most fascinating of the four, as they are triggered by temperature variations on the moon's icy surface. Half of the moon is obscured by darkness for two weeks at a time, and temperatures can drop below -240°F. The temperature rises to +250 degrees Fahrenheit when the same surface is exposed to sunlight again. A moonquake can happen when the frozen crust expands unexpectedly.

Shallow Moonquakes

The most powerful and dangerous for researchers and anyone hoping to populate the moon are shallow moonquakes. These are the only quakes out of the four that have the potential to cause significant damage. The specific source of these shallow quakes is unknown, but they have happened 28 times between 1972 and 1977, with a maximum magnitude of 5.5 on the Richter scale. Like Mars, the problem is that the moon is a celestial body with only one plate and no active tectonic plates.

Scientists believe that the collapsing rims of giant craters (produced by meteor strikes) may be to blame for the shallow moonquakes, which send extended reverberations throughout the surrounding terrain. To put these shallow moonquakes in context, a 5.5 on the Richter scale is enough to shatter plaster and displace structures, which might be lethal for any permanent settlements on the moon, especially since any crack in the oxygen seal could be disastrous for a future colony.

Moonquakes last far Longer than on Earth

Earthquakes on our planet usually last 10 to 30 seconds, although some can last up to two minutes. The longest time on the globe was about ten minutes, but that is highly unusual. Moonquakes don't appear to follow such precise timetables, and they endure significantly longer on average than earthquakes on Earth. When the tectonic plates rumble and an earthquake happens, a massive quantity of energy is released, which travels through the earth's mineral-rich crust, which has been heavily infiltrated by water trapped in the stone. This reduces the power and slows the shaking by making the material somewhat more compressible and absorbing energy and seismic waves.

Things are pretty different on the moon, where the entire ball has been hardened, rigidified, and dried. When a tremor hits the moon's surface, it reverberates loudly because there's nowhere for it to go naturally. A moonquake can persist for ten minutes or longer, with minor tremors lasting for hours.

Until we can further understand the nature of moonquakes, we cannot begin the idea of inhabiting the moon. This would be the first time we as a species begin to colonise the galaxy, and if a sturdy being like the moon proves challenging to inhabit, imagine how hard it will be on planets thousands of light-years away. This is the first step to a much larger mission that we get to make way for – we are living in the most exciting times of our planets life.

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