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Comment by refurb | Hacker News Reader

I’m assuming that USGS picks up lots of ground movement, for example, large blasts from mining operations. They must filter those out based on characteristics? Do companies give advance warning?

Just curious because those instruments must pick up a lot of things that aren’t earthquakes.

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Yes, lots of explosions and other events are filtered out. It's pretty easy to classify large explosions vs. earthquakes both by the depth (earthquakes are rarely so shallow; even a big earthquake that breaks the surface will have most of its energy released 5-15 km below the surface) and by the polarity of the first seismic waves (P-waves) that reach the instruments. In an explosion, all of the waves radiating out will have the 'first motion' being a push outward, away from the source towards the instrument.

However, tectonic earthquakes are rapid sliding movements of the crust along a fault that is a quasi-planar surface. This leads to patterns in the seismic waves, where half of them, two quadrants, show a compressional push away from the source and the other two quadrants have the first motion as tensile, or a pull towards the source. By looking at the geographic locations of the seismic instruments and seeing which show a pull and which show a push, seismologists fit planes separating the quadrants which correspond to the azimuth and inclination of the fault that caused the earthquake.

(edit: deleted ascii art which did not render correctly.

Interestingly, the orientation of the fault and the quadrants of push and pull reflect the directions of the stress field in the crust caused by plate tectonic motions, as well as secondary sources of stress such as gravitational loading of the crust from high topography, or the expansion and contraction of magma chambers under volcanoes. In the 60s through the 80s, geophysicists used this information to put together the first models of the rates and directions of different tectonic plates, but we now mostly use GPS for this.

USGS eventually learn of rock quarries, mines and other things that cause regular earth movements and they tune them out of their reporting. A rock quarry near me used to generated 3.4's a few times a week. I do not know if there is regular correspondence or schedules relayed however.

I'm pretty sure blasting requires some permits. In a sane world I'd imagine blasting permits get automatically funneled into a "booms will be here" list at least at state levels. But then we don't necessarily live in a same world.

They do require paperwork, a lot of it. One of the youtube channels I enjoy watching use every kind of demo material under the sun and they often talk about the paperwork required.

I'm not from usa, but EU. Here, mining operations, quarries, etc. get "booms will be here" licences, with limits (when (usually only daytime), where (quarry/mine limits and how strong the 'booms' are). So for those (rutine, standard blasts), our enviromental (earthquake) agencies don't get the data for each blast (they eg. get data, that company XYZ is allowed to do blasts up to ABC power (KJ or whatever) in location DEF, from 1. jan 2020 to 31. dec 2020 when they have to renew their licence).

Source: friend works as an explosives expert at a quarry

That level of permitting at least let's environmental agencies get data after the fact. If they can get the place and time range of blasts they can filter that out of their measurements. It's probably some poor intern's job. Go through a stack of permits and mark measurements likely covered by the permitted blasting.

I don't know the rules today, but at least in some parts of the US where explosives are used liberally no permits were required at all. You definitely didn't need to inform the government. This likely varies with locale. A considerable amount of explosive in the US is purchased by private individuals for all manner of purpose and use isn't on a formal schedule.

Before 9/11, this was literally a cash and carry business in many States. You could back up a truck and fill it with explosives as long as you had a placard for your truck and a non-sparking liner. It simply isn't practical to track usage in many cases, even today.

Heh. I once wanted to dynamite my car. (It was a heap, and, you know, explosions are cool when you're young, and why not?)

I didn't need any permit. I needed: 1) to prove that I was not a felon, so that it was legal for me to have access to the explosives, 2) permission from the landowner, and 3) to inform the fire department in advance (that was exactly the "booms will be here" list).

Note that this was pre-9/11. Current rules are likely more restrictive.

Only now do I realize I missed my opportunity to blow up random shit with dynamite in my youth.

You've only missed it so far. tomorrow is another day.

https://www.atf.gov/explosives/binary-explosives

> Mixing binary components together constitutes manufacturing explosives. Persons manufacturing explosives for their own personal, non-business use only (e.g., personal target practice) are not required to have a Federal explosives license or permit.

You might need to find a more remote location than a suburban backyard, however, as local authorities may have some objections too.

Also my neighbors and neighborhood dogs.

I still occasionally see "quarry blast" events on the USGS Earthquake web site.

Yes, the USGS filters out several types of non-seismic events from their public feeds, notably including weapons tests.

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