Earthquake Effects & Experiences
It isn't that simple. There is not one magnitude above which damage will occur.
The way an earthquake feels depends on where you are, where the earthquake is, and how big the earthquake is:
"Booms" have been reported for a long time, and they tend to occur more in the Northeastern US and along the East Coast.
Why do earthquakes in other countries seem to cause more damage and casualties than earthquakes in the U.S.?
There is more damage and more deaths from earthquakes in other parts of the world primarily because of buildings which are poorly designed and constructed for earthquake regions, and population density.
Isoseismal maps are maps that show the distribution of intensities from the shaking of an earthquake with contours of equal intensity.
Seismic waves have two main types of effects on groundwater levels: oscillations, and "permanent" offsets. Muddy or turbid water at long distances from the epicenter are most likely an aftereffect of oscillations.
Two sources for photographs that show earthquake damage are:
Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking.
There is nothing different about a cave that would make it immune to the shaking from an earthquake. Just as there are safer and less safer places to be on the surface of the earth during an earthquake, there are also various characteristics inside ca