So if I’m reading this summary in Eos right, there is a new study suggesting that there was significant deformation of the subducted plate in the lead up to the M9 2011 Tohoku earthquake occurred – enough mass was redistributed to measurably change the local gravity field.
There is a mechanical connection between the sinking/subducting plate and the surface – that’s what generates the ‘slab pull’ force that is one of the main drivers of plate tectonics. So a connection – whereby deformation deeper beneath Japan influenced the behavior of the the megathrust near the trench – is not implausible.
However, the normal caveats about stuff like this apply:
finding a signal after the fact for one earthquake does not mean that we can reliably detect such signals before other earthquakes.
finding a potential signal does not mean we can predictably understand what it means.
In other words, we still can’t predict earthquakes.
Analogue sandbox models are a way of demonstrating tectonic deformation processes in the classroom: the weirdness of physical scaling laws means that slowly squeezing and stretching a tub of sand produces faults and folds like those produced in the crust over geological timescales.
Example of a sandbox model experiment where layers of colored sand have been deformed by horizontal compression. Photo by Chris Rowan.Another compressional experiment, but this time with a layer of icing sugar (confectioner’s sugar), which is more cohesive and therefore stronger, beneath the layers of sand, and a layer of glass microbeads, which are weaker, within them. Photo by Chris Rowan.
After building a sandbox model for some research, I wanted to use it in my classes, but the results of the first attempts were… disappointing. The students enjoyed running the experiments, but it didn’t seem to help them understand any better what structures you get in response to different strains, and the effect of weaker or stronger layers.
So, inspired by this article in Eos on cycle-based learning, I developed an activity where we did multiple runs of experiments, with students sketching predictions of what would happen beforehand, assessing those predictions afterwards and also reassessing predictions for experiments that have yet to be run. We kept track of how students’ understanding developed during the multiple cycles by scoring their predictive sketches for how realistic they were. We also tested their general spatial skills with a test before and after the activity.
And we did see improvements! Especially in students who had low scores in the spatial skills test taken before the activity, who did much, much better in the post-test. And importantly, students still seemed to enjoy this more structured activity.
So yes: analog sandbox models are cool, and can be effective teaching tools – if you design an activity that helps students focus on the things you want them to learn.
Model of aftershock rate against time relative to background levels for 300 years after a large megathrust earthquake. Schematic in top right shows relative distribution of core (blue) and corona (red) zones, which are plotted separately. From Stein & Toda (2022).
One think I like about this model is how it reconciles the known history of large earthquakes on the Cascadia megathrust with its historical lack of much seismicity at all, which for some time led us to dangerously underestimate the risk it posed to the Pacific Northwest. It’s still recovering from the last rupture in 1700. Furthermore, perhaps as it starts to evolve towards rupturing again in the future, we might expect to see a bit more low-level seismicity in the ‘core’ region.
This article articulates an increasingly concerning question: in a world where increased exposure to natural hazards, resource scarcity and the consequences of climate change are amongst the most critical issues facing our society, why does Earth Science get no love in our education system?
I spend a lot of time teaching non-science majors basic Earth Science, and it does sting a little when students say they took your class because they thought it would be easy, not because it’s interesting or important. Sometimes, I manage to change their minds, which is quite nice. And my job!
But I can’t help but worry about the many, many people who I don’t even get the chance to convince. Should people having the information they need to make well-informed decisions about the defining issues of this century be dependent on them going to college and taking a non-compulsory course to meet their general education requirements? I’d argue not.
I’m not even sure how you could get such a composition – coalescing from a particularly iron poor planetary nebula, perhaps? But given how Earth’s mantle is dominated by olivine and its pressure-induced phase changes, there could be profound differences in how an olivine-free mantle convects and loses heat.
As this figure from the paper shows, the data also point to another kind of rocky exoplanet rich in periclase (MgO) rather than orthopyroxene. In other words, a significant non-silicate phase!
Figure 3 of Putirka & Xu (2021) plotting estimated compositions of exoplanetary mantles (large diamonds) on one of 3 ternary diagrams. Top left: components are Olivine, Orthopyroxene (Opx) and Clinopyroxene (Cpx), like the Earth’s mantle. Note how the light grey and dark grey diamonds plot way outside the ternary diagram, indicating at least one of the three components is not present. Centre: components are Quartz (replacing Olivine as in Earth’s continental crust), Opx, and Cpx. Bottom right: olivine, Cpx and periclase (MgO) replacing Opx.
So what does this mean? The authors suggest that “quartz-rich mantles might create thicker crusts, while the periclase-saturated mantles could plausibly yield, on a wet planet like Earth, crusts made of serpentinite.”
Of course, there are some sizeable (acknowledged) caveats, given the rather extreme detection method. We’ll have to see whether these inferences stand up to scrutiny. But it’s yet more evidence that beyond our solar system, many surprises about the way planets work await.
Nice plan for content warnings on Mastodon and the Fediverse. Now you need a Mastodon/Fediverse button on this blog.
For lot's more videos on soil moisture topics, see Drs Selker and Or's text-book support videos https://www.youtube.com/channel/UCoMb5YOZuaGtn8pZyQMSLuQ/playlists
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Nice plan for content warnings on Mastodon and the Fediverse. Now you need a Mastodon/Fediverse button on this blog.