Thai insurance WILL cover earthquake damage.
I have a Home Care policy with ThaiSri Insurance. It cost 2100 baht per year for 1.5 million in coverage. Earthquake damage is specifically listed as covered.
It helped me out a few years ago, when an earthquake up near the Burma border caused an underground water line to break. The line was under the house slab, and the entire house had to be repiped - about 20k baht.
Now - I did get paid for all the repairs, but it took some major discussions with their Bangkok office. They tried several dodges to avoid paying.
1. They claimed that there were no earthquakes IN Chiang Mai, so they were not responsible. They even sent data sheets from the Thai Seismological Department "proving" this.
2. They said that they did not believe that all the material I purchased was for the repairs, but out of the goodness of their heart they would pay me 45% back..
I had many conversations with the woman who was head of claims, and kept getting told the same nonsense that her claims people were telling her. I finally sent her links to Reuters and the Bangkok Post for the stories about the earthquake near Burma caused buildings in Chiang Mai and Bangkok to sway, then demanded to speak directly to the claims adjuster that was calling me a thief. They decided to pay up in full.
BTW - the same policy covers equipment as well - so I got paid when a well pump failed.