Hi Chris,

Interesting problem. I was poking around on the USGS Menlo site and I found a report you might wish to review. It's a 30 page Adobe format. The link provided below will lead you to a list of reports and the one I'm suggesting is Appendix F: Estimated Change In State on San Francisco Bay Region On Faults Resulting from the 1906 and 1989 Earthquakes.

This report explains how WorkingGroup99 used various factors in determining stress rates and time dependant factors in determining Coulomb Stress Failure. It gave me the impression your problem perhaps could be viewed differently with this material.

I'm not the least bit concerned about the SAF providing a big one anytime in the near future, but far more concerned with moderate 6.5 quakes occurring on any fault in the SF Bay Area. A recent TV production much like a documentary which ran two months ago said quite plainly "at any time" we could experience a 6.5 on any fault with resulting six foot displacement. When we are thinking of millions of people who commute around the Bay Area on a weekday, one single freeway overpass could cause a delay of up to two days for some people to find their way home. Damage would be severe.

This is our reality and it says we don't need a 7.0 or greater quake to turn our lives upside down. It's a very sobering thought.

Petra

• USGS Open File