In most of my personal experiences and videos seen online, lights seem to go out during strong earthquakes.
Why? I can grab the cord of a lamp and move it around without the lamp turning off, and I don’t think it has something to do with the power company. During earthquakes, some of my friends who live in the same zone or city as me do not experience lights going out.
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A lot can happen during an earthquake. Debris from a poorly maintained building could fall on a power cable, severing it. A panicked driver could crash into a power pole or a power transformer. If the cables are underground, shifting soil or rock could cause them to shear apart, or a burst pipe could cause a short. Sometimes, the ground’s vibrations can even match the resonance frequency of a cable, making it move so violently that it snaps.
As much as a power company or city can plan for an earthquake, there’s always something that can catch people by surprise.
Shaking probably breaks powerlines, knocks down poles, etc. May also cause surges or power fluctuations as grid gets disrupted, etc. and blows transformers and such
Power lines are attached to structures (poles, pipes, walls), and the earthquakes damage those structures.
Aside from breaks in transmission, safely protocols may shut down equipment when they sense an earthquake
Earthquake prone areas actually have detectors on the electrical infrastructure that sense when a severe earthquake is happening. When detected it triggers substations to open their relays. Like a super sized version of the breakers in your house the current is cut off from the grid at multiple points. At the same time the power plants in the severe shaking slow to a stop to remove the source of energy completely.
This is because the movement of the earth can cause high lines to topple over. It can cause buried lines to float in the earth and rupture. And broken power lines don’t just sit there quietly. They whip around as the current in the line causes small explosions from overheating everything it touches. The last thing first responders need to deal with is electrical hazards. God forbid it floods and suddenly the water is energized as well. So for the safety of the survivors and responders the grid is shut off and only reconnected after the experts are sure of the integrity of that section of the grid. More importantly it allows local areas of the grid to respond. So if a far off power plant isn’t in danger from the shaking, the local stations can cut the power and keep the power from the power plant flowing to the undamaged areas.
Now in areas without those detectors the disconnection happens all the same as the moving earth breaks lines damages connections. However unlike the earthquake fail safe system there could still be a path from the power plant to the damaged area. Even worse the power plant may be so far outside the affected area that it doesn’t know a severe earthquake happened and keeps pushing power into the damaged grid. to make it more complex maybe that grid feeds undamaged areas. If you turn off the power to these undamaged areas then you’re just creating new problems to deal with.
Everything is shaking. Electrical outlets are connected via screw type terminals or friction to wires in the wall. If the whole thing is wiggling it may momentarily break the connection.
Same at your main breaker panel
Same at the transformer stepping down power from transmission lines to your main panel
Transmission lines to distribution sites
All the way back to the power plant
Moreover, some high voltage transmission lines are very fault sensitive and may trip due to under or over voltage spikes or ground faults… Resulting in power failures even if all the power lines are actually intact
Speaking from experience here. During the Northridge earthquake, and for several minutes following, we saw at least half a dozen green flashes from transformers exploding (not the Optimus Prime kind). I couldn’t tell you if they exploded because of shaking or hitting against something or overloading, but between them, the lights would sort of start to come back on and then go out again with the next explosion. I assume this was the power grid trying to redistribute power around the bad transformers. It will be interesting to see what happens when more power cables are buried and not up on poles.
Probably the overhead power lines shorting together somewhere between you and the power plant, then the recloser resets the power and power comes back on. Could be nearby trees or other debris falling onto overhead lines causing shorts.
In my area, the diesel generators have seismic sensors that shut the generator down when a vibration above a certain level occurs. They take hours to restart though since these are the steam base load generators.
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