It may seem obvious that underground homes often serve well as natural disaster shelters. This is especially true of the underground homes that are built from concrete and rebar. Some people use wood in their underground homes, but this is not as secure if you’re wanting your house to double as an emergency shelter.
The earth provides a natural barrier to disastrous conditions such as fire, high winds (tornados and hurricanes), hail and other weather-related conditions. Most owners of underground homes know enough to not build these types of dwellings on a flood plain (duh!) or within striking distance of a tsunami as water covering such a house would be problematic.
Underground homes actually provide more shelter from the elements than do earth-berm or earth rammed homes which are typically covered with dirt, soil, and/or grass on 2 or 3 sides. The owners of underground homes will even tell you they feel safer in their house during an earthquake than they would in an above the ground dwelling or building.
Now, this may not be true of those living in cave homes, or other types of homes partially built into the side of a mountain where the weight of the earth may have an impact on two or more sides of the structure. Besides the benefits of lower heating and cooling bills, underground homes also are more secure in regard to thieves and other intruders since they generally have only one entrance and exit which can be secured, watched with cameras and simple alarm systems and defended if need be.
If doomsday ever comes, survivalists living in underground homes can take comfort in the security aspects in living in subsurface dwellings. If you happen to be both a survivalist and a green building advocate, then with an underground home, you can have your organic cake and eat it too.