Your dream has come true, and you are now living on the moon! You start your new job in the morning, so you should get some sleep, but you doubt if you can. After all, you're on the moon! Your suitcases aren't even unpacked yet.
Not that you've been sight-seeing since your arrival, although you have craned your neck to look around as you were hustled from one safety meeting to a technology overview to another safety meeting to... What was with all the safety meetings?
You were thoroughly trained before you left Earth, but these people treated you like a child, repeating the same mantra over and over: "If things start shaking, get into a spacesuit or a rescue pod - whichever you find first - and stay there until you are personally told you can get out."
Shaking? That tiny hint of vibration you felt travel up your legs during the last safety class? That was when the grizzled instructor lunged for a locker and tossed a spacesuit your way as he simultaneously shoved himself into another. He was locked inside his before you could stop gawking and start putting on the oversized thing. You were supposed to worry about that?
He stared at you, didn't even offer to help. Confused and embarrassed, you had just started inserting your second leg when a buzzer went off in 3 short bursts. You could hear it coming through the suit radio as well as the base intercom. You stopped to listen to the voice that followed. "Okay, this appears to be just the normal monthly deep quake, people. It should fade away eventually. But as always, be alert and ready in case it gets worse."
Sound like fun, living on the moon? There's no weather, so you don't have to worry about hurricanes, tornadoes or lightning strikes. There's no tectonic plates, so there wouldn't be any- Wrong! While it is true the moon doesn't have any tectonic plates, it does have quakes.
Scientists are still trying to figure out what causes the 4 types of quakes that happen on the moon. They have figured out 2 causes; the strike of a meteor sets off a quake, and the first thaw after a region has been frozen hard for 2 weeks is another cause.
The quake I spoke of in my little daydream was a 'deep moonquake'. They occur about every 27 days, and are apparently located 700km below the moon's surface. Scientists thought they were caused by the same gravity force that produces Earth's tides, but the computer models are not completely bearing that out. Deep moonquakes might reach a magnitude of 2, which few people feel.
But the ones that a lunar colony would have to watch out for are the shallow moonquakes. 'Shallow' may not sound like much, but the shallow moonquakes have reached a magnitude of 5.5, which can topple heavy furniture and crack walls, here on Earth, in the less than 2 minutes that it rumbles. A lunar colony would have to be built to withstand that kind of torture, because if a wall cracks, it could lose all its air in short order. And you couldn't just stand there and think, "It will all be over in a minute" because on the moon, a quake could last for hours! I think I'd be jumping for the nearest spacesuit or rescue pod for the duration.
And here I was thinking of building a colony under the moon's surface! For a story, of course.