From my understanding
underground shelters tend to fair batter in earthquakes than above ground structures since the underground building will move with the earth as it is part of it while above ground structures tend to stay still and the earth moves from underneath it. One of the first suggestions for preparing a home for earthquake resilience is to tie it to the earth. While this might seem counter intuitive, especially when giant buildings are given shock absorbers to isolate them from a quake, imagine the ground under a home shifting without the home being secured to the ground. if the earth moves to the sides or drops the house is standing stationary at first and then reacts after the fact to the new conditions like dropping to meet the now lower ground, or being hit by the ground coming at it from the side. If however your home is tied to the earth (as an underground home would be) then as the earth moves so does the home. While it might not be comfortable to be in a quake in an underground home, from my understanding if built well it
should be safer than standard above ground homes.
"Where will you drive your own picket stake? Where will you choose to make your stand? Give me a threshold, a specific point at which you will finally stop running, at which you will finally fight back." (Derrick Jensen)