If an Earthquake is an giant plate moving, why is the epicenter a single point and not the entire fault line?
In: Physics
First, we need to make sure we know what an earthquake is: it’s the buildup and sudden release of energy causes by two tectonic plates interacting with each other in any direction.
The boundaries between tectonic plates are not a clean, uniform “slice” like you would make in a cake. The boundaries are more like what you see if you dropped a dinner plate and it cracked in half. The edges will be random and have parts that go to one side or the other. Still, for the most part the plates interact smoothly, and areas that sit on top of them have multiple “micro quakes” on a daily basis, as the plates move. Sometimes, however, there is an interaction between the two at a point where neither side is able to move; this causes a buildup of (potential) energy. When one side finally gives way, there is a release of energy from that single, relatively small point, which is the “epicenter”. This release of energy causes shockwaves (for lack of a better term) to travel outward from the point of release, kind of like ripples in a pond; those waves are the actual earthquake
earthquake is caused by vibration from two plates hitting each other.
like if you smack a hammer on concrete. The whole hammer isnt the source of earthquake / vibration in the concrete, just the spot where hammer hit the concrete
The plates are elastic, and jagged at the boundaries, when they move across each other the pointy shape of the edge means they get caught up at certain spots, the slow motion of the plates causes tension to build up at the snag until friction cannot hold anymore and it lets loose all at once in that spot; the epicenter,
When the edges of the tectonic plates press against each other, the bedrock at the edges may shift or crumble, but certain areas build up potential energy.
Eventually that energy can be released violently in bursts creating earthquakes and aftershocks. These geological vibrations actually occur along a lenglth of the fault or at multiple points, but the epicenter is not necessarily the “point of origin” of an earthquake. Rather it is the averaged locus of activity. It would be impractical to try to relate all the data of relative motion along the fault to the layperson, so the “epicenter” is the approximate middle point of the area affected by geological turbulance.
Lots of over complication going on here. Earthquakes involve movement along a fault plane. The epicenter is the point on the ground above where that movement begins.
It’s like when you’re pushing something really hard, nothing is moving, and then when it moves you go slicing except the plates don’t slide as much and just sort of grind against each other really hard
Think of sliding two uneven pieces of wood past each other. One piece gets snagged on the other. You keep applying force, eventually the spot where they are snagged breaks and the wood moves quickly. This is an earthquake along a transform boundary like the San Andreas fault. The spot that snagged is the epicenter.
You know how when you spin one of those raffle wheels, the little pegs hit the pointer and eventually it slows down and sometimes at the very end, a peg gets kind caught on the pointer and it holds and holds and holds and there’s all this tension. Will it go? And then it loses its hold and the wheel makes that last tiny turn.
The wheel is a tectonic plate and that last peg holding it up is the epicenter. The whole wheel moves a tiny big but the pressure holding it back and then releasing is all right there.
Where is my favorite Redditor /u/theearthquakeguy?
Put your damp hand down on the counter top with a fair bit of downward pressure and then start trying to slide it across the counter. You’ll notice it doesn’t move all at once, but little spots let go and then stick again and another spot moves in a really jerky way. This is same idea.
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