First, this is what you get when you have a GA Junkie that has just turned in his course grades and now has a bit more time on his hands…

Second, if you are coming to the Presbyterian Church (U.S.A.) General Assembly in San Jose from some place else in the country where you don’t worry about earthquakes and the thought of earthquakes may be worrying you, you may not want to continue reading.  On the other hand, “knowledge is power” and having this info may help calm nerves.  (And you can think of that “may” in our polity sense.)

In case you haven’t caught it from one of my previous posts, my day job includes earthquake geology.  And you might have noticed in the GA Program that on Monday afternoon there is “Mission Tour 4: Hike through earthquake country” that includes a visit to the San Andreas fault.  (And no, I’m not planning on going since I’m there for the GA business.)

On the plus side, I would encourage you to be aware of earthquakes and be prepared for them.  The mantra here is “Duck, cover and hold,” although I joke with my class that “Don’t Panic” works too.  That is duck under something solid, cover yourself with that solid object, and hold on to it so it does not shake away from you.  Standing in door frames is not the current preferred safe zone since we finally figured out that most door frames also have a door attached to them and sometimes that door wants to use the frame with you so people were getting hit by the door.  If you want more info, the standard reference around these parts is “Putting Down Roots in Earthquake Country,” and check out the San Francisco edition.

If you want more info:  There is the real time earthquake map of the San Francisco area and a slightly different map with more around San Jose.  There is also a page on Bay Area Earthquake Probabilities from the USGS.

Around here we usually calculate probabilities on a 30 year time period, as in there is a 99.7% chance that California will have a magnitude 6.7 or larger earthquake in the next 30 years.  And around here that is not called a forecast, that is a reminder.

What about for next week?  Well the good news is that there has not been a large one in the area for a while so there are no really active aftershock sequences to provide any shaking.  As for regional quakes, based on regional probabilities there is about a 10% chance that the San Francisco Bay area will have a magnitude 4 or larger earthquake in any given week. (If you want the gory details, the G-R magnitude relationship, based on the last 20 years of seismicity, is log N = 6.04 – 1.33 M.  N is the number of earthquakes in a year larger than magnitude M.)

But “California does have its faults” and San Jose is sandwiched between the big ones in the Bay Area: the San Andreas about 15km to the west and the Hayward and Calaveras faults about 10km east.  Running some rough numbers based on the State of California fault information for the area the San Andreas fault to the north and to the south, if treated as separate earthquake sources, could each produce something a bit over a magnitude 7.  No surprise here since the 1989 Loma Prieta Earthquake was a 6.9 on that southern segment.  The Calaveras and Hayward faults are about the same.  But the closest fault to the west is the much less active Monte Vista thrust fault about half way to the San Andreas.  Add up all their probabilities and you get about a 0.03% chance of having a large earthquake on one of these faults in the next week.

So there you are — Welcome to California.  And I’ll see you there.

Then
a great and powerful wind tore the mountains apart and shattered the
rocks before the Lord, but the Lord was not in the wind. After the wind
there was an earthquake, but the Lord was not in the earthquake. After the earthquake came a fire, but the Lord was not in the fire. And after the fire came a gentle whisper. – I Kings 19:11b, 12 NIV