M 7.1 SoCal Earthquake: What's Next?
temblor.net
temblor.net
While the magnitude value signifies the overall energy of the quake, intensity scale values indicate the shaking intensity of a given location; hence, it feels more grounded in one's daily life experiences. Many Japanese individuals have developed an approximate sense of how strong a quake is - conversations like "That was a bit big, somewhere around shindo 4?" are common after quakes. People do of course care about magnitude, but the thing they care most about after a big quake is more likely "what was the seismic intensity in the worst-hit area?"
Any idea why intensity scales seem to be much less common in the US?
[1] https://en.wikipedia.org/wiki/Japan_Meteorological_Agency_se...
[2] https://en.wikipedia.org/wiki/Modified_Mercalli_intensity_sc...
In fact the Earthquake Early Warning's "next steps" plan says "New sensors need to be added in California to shorten the CISN sensors spacing to approximately 12 miles to facilitate timely EEW. The shorter the station spacing, the smaller the blind zone will be because warnings can be issued faster."
Check out this map comparison of the two networks: https://earthquake.usgs.gov/research/earlywarning/images/sta...
https://earthquake.usgs.gov/research/earlywarning/nextsteps....
I went to school in the LA Inland Empire area - there was a quake I felt last year there during class. It was really close but I'm pretty sure it was just short of 4.0.
We have hundreds (thousands?) of quakes per year, but the likelihood your average resident feels a quake in any given year? I think it's low.
The only time I've felt the ground shake was in the earthquake simulator at the California Academy of Science in SF :)
Friend of mine that lived in Oakland during the 89 earthquake mentioned seeing a 'line' of damaged buildings that snaked through a neighborhood. One or two houses on a block were wrecked. The houses across the street were also wrecked. Houses next to them were fine. Go the next street over same thing.
He thinks that line followed an old creek bed that developers filled in. So those houses were built on mud overlain with poorly compacted fill. During the earthquake the mud liquefied and sloshed around and the fill settled.
Flip side, friend in the Santa Cruz mountains a couple of miles from the epicenter. His house is built on top of a hard shale outcrop. His house suffered no damage at all.
One striking effect was the directionality of the damaging waves. Bookcases and such that were perpendicular to the waves from the hypocenter went over; those that were parallel were fine.
[1] https://heavy.com/news/2019/07/ridgecrest-earthquake-damage-... https://losangeles.cbslocal.com/2019/07/04/6-6m-quake-strike... https://edition.cnn.com/us/live-news/earthquake-california-j... https://www.cbsnews.com/news/ridgecrest-earthquake-aftershoc... https://www.latimes.com/local/lanow/la-me-ridgecrest-earthqu...
It seems to me like we've recently (~15-30yrs) had a lot of new technology deployments (and accessibility to the underlying data that's produced) which might considerably help us with gaining an understanding over time. Things like high-resolution, high-precision aerial & satellite radar/lidar/photography and the like.
I tend to think it's just a function of time at this point, but on geological time scales that may still take quite a while I suppose.
1. Hold your hands together, palms open, as if you were praying.
2. Press them together very hard, and at the same time try to slide them past one another.
3. Predict exactly when they will slip, by how much, and how loud the sound will be. To be roughly to scale, it must be with millisecond [0] and millimeter [1] accuracy.
[0] Assuming avg. 100 years between quakes, prediction accurate to a week, avg. 5 seconds before hands slip, then 100 yrs * 52 weeks : 1 week ~ 5,000:1 ~ 5 sec : 1 msec.
[1] A 150 KM fault with a prediction of slip accurate to 0.5 M movement is 300,000:1. For a hand span of 150 mm that would equate to 0.5 um. On the other hand (pun intended), we could compare maximum slippages; assuming an earthquake movement max of 20 M and a hand slippage max of 0.2 M, a real-world resolution of 0.5 M would equate to a hand-slip prediction accurate to 2 mm.
Anything is possible, but I’m not saying we can’t or shouldn’t fight it or take steps to prevent it or mitigate damage from it. I’m saying no point in being worried about it.
(sorry there is no reply option for lots of pulp).
Isn't worry the one human emotion that actually makes us ready for things. If we had an earthquake 1000 years ago that killed half of society and the people just said, damn oh well. They don't do things the same way after that do they? They change design, learn more about the planet, adjust adjust adjust. All of that is driven by worry.
Then prediction research became the black death of academic careers with little progress.
This century a milder version called 'earthquake forecasting' has gained acceptance. That is more big data and statistical odds.
Plus 'early warning' seeks to detect quakes and warn people at the speed of light, seconds before damaging waves arrive at the speed of sound.
“There was plenty of accumulated stress, enough to permit a quake with 3 m (10 ft) of slip. That suggests that one can, indeed, have aftershocks 150 years after very large mainshocks”
I looks like quakes are on a continuum. The extremes are, each quake is an individual event; on the other all quakes are a result and continuation of previous quakes. It seems like the slider position on the continuum is up to a bit of “interpretation”.
Thus, you can have multiple points of stress all linked where it’s not obvious which one is going to slip first, but they are likely to cluster over relatively short periods. Where 100 years can still be considered short.
However Dr Stein is one of my Stanford classmates and computing earthquake stress changes for 30 years. So I would believe this study.