Yesterday, we had a non-trivial 6.0 earthquake over near the Nevada border, in a thankfully very thinly populated area, as discussed here. Nobody was hurt, and I’ve heard of no significant property damage. My question: it seemed to me that the number and intensity of the aftershocks was higher than usual. Was I simply succumbing to recently bias, forgetting how previous aftershock maps looked? The USGS does aftershock forecasts for most 5.0 or larger earthquakes. Here’s their forecast for yesterday’s quake.
According to our forecast, over the next 1 Week there is a 3 % chance of one or more aftershocks that are larger than magnitude 6.0. It is likely that there will be smaller earthquakes over the next 1 Week, with 10 to 53 magnitude 3 or higher aftershocks. Magnitude 3 and above are large enough to be felt near the epicenter. The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily.from the forecast linked to above
Just counted them up: there have been 41 magnitude 3 or higher aftershocks within 20 hours of the quake, way over the lower threshold and nearing the upper threshold for the week’s worth of forecasted activity. Unless this thing calms down a lot pretty quickly, it’s going to push significantly past those numbers. There have been 136 2.5 or higher aftershocks so far, including 13 in the last 4 hours. So, slowing, but still pretty active. (SEE UPDATE BELOW- I DIDN’T UNDERSTAND THIS CORRECTLY)
Is this anything to worry about? Nope, at least, no more than usual. Predicting earthquakes is still very much a very broad and inaccurate proposition. Predict a major quake in California sometimes over the next century? Pretty safe bet, especially since you won’t live long enough to face the consequences of getting it wrong. Anything much shorter than that? Seems likely, based on prior experiences, but, like the brokers say: past performance is no guarantee of future results.
Maybe, inch by inch over the next 100 million years, much of California will fall into the ocean, in the sense of becoming something like an island. This is assuming the whole eastern slope of the Sierra thing is where the real action is. The San Andreas Fault is where costal California from just south of San Francisco all the way down to the Sea of Cortez is moving north relative to the rest of the state. If this continues (no guarantees, remember) L.A. will end up a suburb of S.F. well within 100 million years. Doesn’t seem to be any falling onto the ocean action there.
On the other hand, the relatively new Sierra Nevada range, only about 10 million years old, was pushed up (they say) by a process of rising magma along its current eastern edge, thinning and lightening a huge block of granite crust, which then ascended to its present great height. The western edge is like the base of a pivot, as if a gigantic 40,000 foot thick granite table had been lifted along the eastern edge – which is pretty much what happened. Along the western edge, the slope if fairly gentle, except where glaciers carved it up, most famously in Yosemite:
On the eastern edge, it’s crazy-steep. It’s even more extreme that it appears, because the terrain at the base is something like 5,000′ high, so you only see an 8,000 foot change in elevation, while you get the full 14,000 ascending from the west.
Back to earthquakes: the Sierra is still rising. Hot magma is still there under the surface along the eastern slope. The crust has been shattered from east of Bakersfield up to north of Tahoe, with historically huge quakes – an estimated 7.9 back in 1872, in Owen’s Valley, where the valley floor dropped 20′ and a new 86 acre lake was formed – occurring with geologic regularity along dozens of faults.
And then there’s the Long Valley Caldera, formed during what would now be a civilization-ending volcanic explosion 760,000 years ago. Geologist don’t think that is likely to happen again, but my confidence in that prediction is tempered by geologist not having much of an idea for how the volcanism in the area happened in the first place.
Anyway: doesn’t seem this earthquake portends the End Times. I have mixed feeling about this, as, on the one hand, I haven’t gotten this year’s apricot crop in yet. Among other unfinished business. On the other hand, I’m ready to see this clown show end.
P.S.: another 7 2.5 or better aftershocks hit while I was typing this up, including another 3.0. So there is that…
UPDATE: The USGS forecast is – odd. The ‘over the next 1 week’ part is not over the week following the earthquake, but rather over the week following the forecast publication date and time. The forecast is updated regularly. This means that the total I was counting up, from the earthquake to now, does not tie in any way to the forecast numbers. The forecast is forward looking as of roughly now, and is useless for any historical comparisons. I guess that makes sense for a public-facing document, where people might go (layers deep into a government website – yeah, that’s where everybody’s granny is going for her info…) just to see if they should expect to feel anymore earthquakes (3.0 being the smallest earthquake anyone can feel under anything less than ideal circumstances.)
So, to whine a bit: here we are, at the nadir of public understanding of science in the West since maybe 900 AD (not kidding), and a page very narrowly useful, and to only a very small subset of people, is located somewhere where only very curious and somewhat search-savvy people can find it. How’s that supposed to work to anyone’s benefit? Now, while my proposed use of the data is, if anything, even more obscure, at least it’s conceptually simple. That any significant number of people would be interested in the data as presented beyond the blanket reassurance provided by the super-high-level summary – there will probably be some small quakes over the next week or so, gradually tapering off. The chances of another bigger quake are small- requires a faith in the curiosity of the American public that is not seen in reality.