Last week ceramic tiles from both my parents house and my sisters house popped up . What is the likely cause?

Last week ceramic tiles from both my parents house and my sisters house popped up . My parents house is some 85 feet from my sisters house. The section of her house where the problem happened is a porch area facing north and in the case of my parents house its on the north side but their living room and dining room, the only rooms on that side of the house with ceramic tiles. My parents house was constructed in 1962- 63 with concrete floors and walls, the concrete floors are suspended. In the case of my sisters house that section of her house although concrete floors but not suspended but filled. He house built in 1984. From a birds eye view looking down at the houses it looks like this problem is almost in a straight line. Could this be the result of seismic activity? Our area not known for such as its a rarity in the island and no current construction under a half mile of the houses, as I checked for all these possibilities. What is the likely source of this problem?. The line if extended does not intersect any other structure just lawn street or garden area so cannot observe any crack line etc.