That was a magnitude 6.9 earthquake. For context, it has been speculated (source: https://www.newyorker.com/magazine/2015/07/20/the-really-big... ) that the next "really big one" could be in the range of 9.0.

> If the entire zone gives way at once, an event that seismologists call a full-margin rupture, the magnitude will be somewhere between 8.7 and 9.2. That’s the very big one.

I'm not well-versed in earthquakes, but from what I know the Richter magnitude is logarithmic in scale, I can't really even imagine in my head what a 9.0 quake is like.

I'm glad OP / someone is asking these questions, I often wonder about this myself, being a tech worker in San Francisco.