Thread by @mikamckinnon

This is a very popular question where the answer is frustrating because it’s almost, but not quite, the right question.

Simple version: False.
Thread for complicated version.

https://twitter.com/yashar/status/1307803946480619520

All active fault zones move.

While a particular fault may be locked or have locked segments, overall the tectonic plates that make up the surface of our planet move at roughly the same speed fingernails grow.

We have thousands of earthquakes a year, most too small to feel.

But the difference between tiny harmless earthquakes and big damaging earthquakes is nontrivial.

We describe earthquakes a lot of ways: magnitude (amplitude of seismic wave), energy released, intensity (severity of shaking)...

Details: usgs.gov/natural-hazard…

Each step up in magnitude is x10 in amplitude, but x32 in energy released. That means it’d take 31,623 magnitude 3 (M3) earthquakes to release the same energy as a magnitude 6 (M6).

Calculator: earthquake.usgs.gov/education/calc…

A nearby M3 or M4 earthquake doesn’t cause significant damage, but it does feel like a giant slapped your home. It’s a scary, sharp jolt.

If you had a few hundred of them, it’d only release a fraction of the energy of a M6.

This gets you to the “Nah, not really” answer.
But...

The real problem is that for all the teasing about geology being the simple science, real-life rocks are complicated.

Plate tectonics don’t reliably march along at an unwavering pace, steadily building up stress. We don’t even understand what exactly drives tectonic motion.

We know that when enough stress builds up, rocks break & fault slips. Large-scale hand-waving, we got this covered.

But, uh.
Fracture dynamics are hellishly complex.
Forecasting how & where a fault will slip next is a Very Complicated Question that gets worse the closer you look

If a fault isn’t moving AT ALL, yeah, it’s a probably bad thing.

But not due to small quakes bleeding off energy because it’s SO LITTLE energy on the scale of problems.

Instead, it’s because if a fault doesn’t move at all, it gets buried & hidden. And then it surprises us. Eek!

(“probably a bad thing” expanded:
It could be a fault zone has gone inactive! Tectonic plate boundaries can deactivate or change directions, because... uh, reasons? TBD.

But even inactive regions can still have damaging quakes as rocks settle like a creaky house.)

But!
On a human scale, it can be handy to have small earthquakes.

I’ve lived in California and the Pacific Northwest. Both get earthquakes, but for different reasons of different magnitudes on different timescales. This hugely impacts public perception & preparation.

California is a strike-slip tectonic boundary of fairly frequent moderate quakes. That means shallow side-to-side motion produces M6-7 quakes every decade-ish.

PNW is a subduction with infrequent huge quakes. This means diving motion produces M8-9 quakes every few centuries-ish.

Most Californians have experienced an earthquake, and almost all know someone who was in a major California quake. (hi! I was in ‘89 Loma Prieta!).

They’ve had reason to Drop! (or Lock!) Cover! and Hold on! They have first-hand motivation to do basic seismic safety & quake kits.

Most PNWers haven’t experienced a significant earthquake. We know we’re on unstable ground in theory, but it’s really easy to forget on a day-to-day basis.

The last Big One was January 26, 1700. It’s legend, with scattered oral histories among our local First Nations.

Wee quakes don’t release enough energy to prevent larger quakes, but they can improve personal preparedness & public support for seismic mitigation, and help us identify faults so we don’t accidentally build on the worst possible places.

So yes, they’re better than NO motion.

Even more fascinatingly, a not-insignificant number of earthquake injuries and fatalities have nothing to do with physics or engineering, but with psychology.

People panic.
They stress themselves into heart attacks, or try to “run to safety” and get hurt.

Smaller quakes are a live-action drill, a chance for people to make mistakes without enormous consequences.

Even if they have a heart attack, a smaller quake means less infrastructure damage and other injuries, thus better chances of timely medical intervention saving them.

Geologically speaking, small quakes do approximately fuck-all to delay larger quakes.

But from a human perspective, small quakes are invaluable for preparation.