My house here in Mexico is rather earthquake proofed. But, the big problem with earthquakes and stone houses, or I guess any kind of house, is resonance. An example of resonance is when you hum at a guitar, you can feel the vibrations.
Earthquakes have random frequencies mostly from less than 20 hz to 2000 hz. My house has reinforced vertical and horizontal beams made by creating a network of 1/2 inch rebar wired tight, and put in forms then filled with concrete mix.
Okay, that is strong. But, the distance between the beams has to be short enough that the wavelength of the frequencies do not resonate that section of the house.
Resonance will literally shake a building to pieces, even if somewhat strongly built.
When we have an earthquake, I saunter to the door, but not until I have my pants on. This house is not going down unless the area is totally flat.
Those stone buildings in Italy perhaps do not have any vertical and horizontal reinforced beams, though that is a guess knowing about buildings here built that way.