and not just during earthquakes.
People move. If you do genealogy you'll find that people move around, which is a pain in the butt locating people. The Help comes from a line of lumberjacks, who ran around the northern US border following trees, and they had a common last name. So it is a guess which state they were in for any given census. My people in NC, though staying in the same two counties, moved around those counties, a lot. So that comes in mind when people say gentrification moves people out of their homes. Life moves people out of their homes. Americans are movers with fantasies that they are stable.
Most people move. A few stay, but in time they move too. In the arguments over gentrification the one family that has been in the same house for 30 years, but easily forgotten are all the other people on the street who stayed for 1 -5 years and moved. Some a few blocks over, some completely out of the neighborhood. Moving people are a bit of a problem for me with the census project as I look at the city directories, which you can find on-line in Google Books: Boyd's directory of the District of Columbia, 1892 and Boyd's directory of the District of Columbia, 1903. I can't speak to the accuracy of these sources as I don't know how the data was collected, but it's the best source out there, short of hopping in a time machine. In my own house there were one set of people in 1892, then in the 1900 Census 11 people, then in the 1903 directory one person, all with different names. Considering that many people were renters, there really wasn't anything tying them to one house, thus freeing them to move