The way an earthquake feels depends on where you are, where the earthquake is, and how big the earthquake is:
- A large earthquake nearby will feel like a sudden large jolt followed quickly by more strong shaking that may last a few seconds or up to a couple of minutes if it’s a rare great event. The shaking will feel violent and it will be difficult to stand up. The contents of your house will be a mess.
- A large earthquake far away will feel like a gentle bump followed several seconds later by stronger rolling shaking that may feel like sharp shaking for a little while.
- A small earthquake nearby will feel like a small sharp jolt followed by a few stronger sharp shakes that pass quickly.
- A small earthquake far away will probably not be felt at all, but if you do feel it, it will be a subtle gentle shake or two that is easier to feel if you’re still and sitting down.
The type of crustal material the seismic waves travel through on their way to you, and the type of shallow crustal structure that is directly below you will also influence the shaking you feel.
Soft thick sediments will amplify the shaking and hard rock will not.
If the energy happens to bounce around and get focused on where you are, that will also amplify the shaking.
Low-level vibrations that last for more than a few seconds is not indicative of an earthquake, but is more likely a man-made environmental source.
Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking.
Liquefaction occurring beneath buildings and other structures can cause major damage during earthquakes. For example, the 1964 Niigata earthquake caused widespread liquefaction in Niigata, Japan which destroyed many buildings.
Also, during the 1989 Loma Prieta, California earthquake, liquefaction of the soils and debris used to fill in a lagoon caused major subsidence, fracturing, and horizontal sliding of the ground surface in the Marina district in San Francisco.