This area has been seismically active for a long time. Just a matter of time before an event like this happens. The homes sit above a nature preserve that was never developed because of the land movement. The Portuguese Bend is a road that needs constant repairs. Some people just dared to live on top of it.
I used to mountain bike that preserve, but many of the trails closed from the slides. It may someday become an even bigger preserve now.
These arnt related to seismicity. This is dirt moving via loading and rain fall lubricating a natural slip plan. And has been moving for many decades. Typically to keep these things together they need very deep pylons and tiebacks and the rest, but it's unlikely developers want to spend more than needed on things no buyer sees.
I used to mountain bike that preserve, but many of the trails closed from the slides. It may someday become an even bigger preserve now.