It's also worth noting that a mag 8 is about the maximum expected from the San Andreas fault, a strike-slip fault, and most quakes come in well under that. The two largest quakes I'm aware of, the 1906 San Francisco and 1857 Fort Tejon quakes, were mag 7.8 and 7.9 respectively.

Significant damage can be experienced starting at about mag 6, though that tends to be pretty specific (individual structures, often pre-dating earthquake codes, and locations on poorly-suited terrain such as riverbottoms, reclaimed wetlands, or sand). Widespread general damage would only be experienced with larger quakes (mag 7--8).

Japan has a significantly higher risk of mag 8--9 quakes. The 2011 Tōhoku quake was a magnitude 9, which is 100 times more powerful than a mag 7, and over 100,000 times more powerful than this morning's temblor in Berkeley. Japanese faults include subduction zones and considerable tsunami risk.

Similar risks exist between the California-Oregon border through to British Columbia on the Cascadia Subduction Zone, and could similarly product a mag 9 event.

<https://en.wikipedia.org/wiki/UCERF3>

<https://en.wikipedia.org/wiki/Cascadia_subduction_zone>

> a magnitude 9, which is 100 times more powerful than a mag 7

That is actually 1,000x more powerful. For historical reasons, the magnitude scale is 10^1.5 between whole numbers.

The Cascadia earthquake in January 1700 produced a tsunami that traveled all the way across the ocean and hit Japan with 16-foot waves. That's what mag 9 looks like.