Who said anything about a magical safety radius?
My point was you posted a list of earthquakes of magnitude 9.4 down to 7.7 as if there were simply comparable, which they aren't.
Then the factor of the distance from the epicentre determines, to a large extent, the chance of damage, the further away the lesser the likelihood of damage or casualties. But the underlying geology is a significant factor, in the case of Bangkok this is unconsolidated coastal marine and lagoon sediments, unconsolidated sediments serve to amplify the ground motion. Which is the reason an earthquake over 1000km away was still damaging.