Without getting into the general argument here, I'm just going to dispel a few misconceptions about earthquake engineering: No one (basically) who is involved

Without getting into the general argument here, I'm just going to dispel a few misconceptions about earthquake engineering: No one (basically) who is involved in earthquake engineering would ever use the term 'earthquake-proof' to describe one building, much less an entire country's construction practices. Instead, we generally design buildings to not require any repair after earthquakes which occur more frequently than once per century, and design buildings not to fall down after earthquakes which occur more frequently than once per 2500 years. There is always a chance that an earthquake will occur outside of those limits, and nothing is designed to withstand those. While you are correct in assuming that adding weight to a structure (all things being equal) will increase the seismic forces it experiences, the contribution of sound insulation to the weight of the building is pretty insignificant. And for lightweight structures it is much easier to increase their strength than to decrease their weight. Third, earthquake resistant 'technology' [re: design practices] is not as ever-changing as you might think. While there are some examples of innovative solutions like putting water tanks at the top of skyscrapers, for low-rise structures there really isn't that much to it. If you take a 100 year old house, screw some plywood sheets between the floors, and bolt it to the foundation, then it will be 90% (estimated) as safe as a brand new house. Earthquake resistance is not so much about technology, and is more about making very sure that all of the force generated in the house can make it to the ground without breaking anything (though physicists would say that the force goes in the other direction from the ground to the structure). This means that earthquake safety is fairly proportional to the amount of time and money spent on construction, which is very much not incentivized by disposable construction.