What kind of damage would happen in a 6.0 earthquake that happens for 20 minutes?

Answer 1

It would depend on where you were. The closer you were to the epicenter the more damage you would see. Also, if the focus of the earthquake were deep underground it would cause much less damage even at the epicenter. A magnitude 6.0 earthquake (assuming you are using the richter scale) for 20 minutes would knock down poorly built homes/buildings and could cause serious damage to roads and bridges that are on unstable earth. Sandy areas are much less stable so a structure on top of this unstable ground would be more likely to be damaged.

EDIT:
David gave a very good answer, but I need to point out that the epicenter is never "deep" as it is the place on the surface of the ground directly above the focus of the quake. It is a common mistake, but it is important to be accurate.

I looked at this question as a hypothetical - and while a magnitude 6 earthquake is fairly minor, if the ground shook that much for a full 20 minutes it could very well knock down buildings that are built on poor foundation or are otherwise structurally flawed. Shifting of soils beneath roads and bridge foundations would very easily cause severe damage to the roads/bridges (if a road cracks in half and there's a 6 inch lip it makes the road useless, and a bridge that is not on secure footing is very dangerous).

That being said - the other answers are correct in saying a single earthquake would not last 20 minutes.

Answer 2

The quake at 6 on the Richter scale would be unlikely to do very much damage unless it was right at the surface. Quakes that do damage are usually seven or above.

Where the epicentre is deep the effects would be much less.

Quakes are over fairly quickly. The P wave arrives first giving a slight shake and often disturbing the air so that a sound is produced. This is followed by the S wave which is characterised by the surface rolling or heaving and this is what causes the damage.

Where a magnitude 6 quake might cause severe damage is if it is out at sea and causes a shift in the sea bottom. Then it may cause a tsunami which would devastate the coast.

Answer 3

The ground doesn't shake for 20 minutes, hon. There is usually a big jolt, ---it will rattle your house, break some windows, even bring down a chimney --then a series of smaller ones over the next several hours or days.