The 4.5 earthquake in CA was no surprise to me thanks to the earthquake forecast site Dutchsinse. Google, "Dutchsinse 5/6/2018 10 pm forecast" to watch this gifted guy (who is far more knowledgeable regarding earthquakes than the whole lot of USGS seismologists lumped together)! Seismic energy transfers along plate boundaries/ fractures/craton edge.
This year has already seen many large disastrous earthquakes and shock waves. It seems silly to assume that there is no way that one of the most earthquake prone cities in the world is unlikely to suffer from one soon. The real question is when and how dramatic it will be.
There is no way to predict an earthquake but it would seem likely. San Francisco is not immune to earthquakes. And if the plates nearby are shifting, it could easily be a problem for them soon. However, the bottom line is that when and where earthquakes will strike is still an elusive item to predict.
I don't believe that San Francisco is any more likely to suffer an earthquake than anywhere else in the world. The last earthquake in San Francisco was in 1906, which is more than 100 years ago. I think this means the area is not very prone to earthquakes and there won't be one anytime soon.
Earthquakes in one place doesn't necessarily mean that there will be earthquakes in other places. San Francisco has had earthquakes, very severe ones, at various times throughout history. They have not been able to come up with a pattern or any kind of way to determine how to predict when one will hit next.