SAN RAMON, CALIFORNIA – We promised last month that we wouldn’t report on every single tiny earthquake that hits the 925.
And we’re glad we made that promise, because in the last month, the USGS reports that there have been at least 100 such quakes in the San Ramon area alone. Two resulted in notable shaking, at 3.6 and 3.1 magnitude
So, does all this small earthquake activity mean a big one is on the way? We took at a look at official guidance and estimates from the USGS to try and get some clarity.
What’s been “shaking” in the 925 lately
The recent action that many East Bay residents have noticed is coming from an active fault system that runs close to us, including the Calaveras Fault Zone. Seismologists describe the latest run near San Ramon as a swarm — a cluster of small quakes that pop off in the same area over a short period of time.
There’s also the Concord Fault, which runs through (duh) Concord, but also Walnut Creek. It’s been less active this month.
So, does the activity on these local faults mean anything?
Perhaps frustratingly, no one can really say. The USGS is quite blunt about the fact that no one can predict earthquakes.
That means swarms, being “due for the big one”, animals who act strangely–none of these things are reliable indicators of a quake on the way.
It’s possible that a small swarm someone precedes a big quake, and indeed there’s such thing as a “foreshock”, where a small quake happens in advance of a bigger “aftershock.” But again, on the question of whether these are tied to earthquake swarms, the answer is that no one really knows for sure.
The Big One Is Almost Certainly Coming (Soonish)
So what can the USGS tell us? They can’t predict specific quakes, but they can say a lot about the chances of a really large quake happening in a specific timeline.
For the Bay Area, the relevant timeline is the period 2014 to 2043. The USGS predicts a 72% chance that we’ll have a 6.7 magnitude or larger quake in that timeline.
So while this month’s swarm probably doesn’t mean anything, if you plan to live in the Bay Area for the next few decades, you’ll almost certainly be here with the “big one” arrives.
Luckily, you can take steps to be ready. Have a source of backup power, secure heavy items, keep a “Go Bag” and food and water handy, and know basics like how to shut off your gas in the event of a quake.
We’re still not going to report on every tiny quake. But it’s important to know that a big quake could be on the way in the next 20 years or so, and to plan accordingly to stay safe.
