Last session my players entered a facility fueled by Azzy blood magic, and destroyed large chunks of it with C12, destroying buildings an magical items. It was done in the middle of Salish/Shidhe land, and I am trying to determine effect.

1. How much C12 would have to go off for it to register on a seismograph? Is there a formula?

2. How about astrally? Seems like the detonation of powerful magical artifacts should send ripples through Astral space, but I'm not sure how to represent that. One effect the PCs noticed is that during the explosion, they were able to see an Azzy temple where the lab the demolished once stood (at least for a moment or two).

Clearly the Azzy's will have noticed, but how much C12 would have to go off before the S/S council noticed the explosion?

It comes in 12 now?

<-- Knows dick about military explosives

Anyway, I'd say they'd figure it out, even without seismographs, on account of the big smoking crater, destruction/smoke clouds visible to drones/spy satellites/thermal & atmospheric sensors/normal sight, freaked-the-fug-out spirits fleeing the scene screaming "Holy F&%k! You won't believe what just happened!!!" to anybody with even a pinch of astral perception, ect...

Define "register on a seismograph". How far away is the seismograph? How much do you need it to wiggle the needle before you're satisfied? A couple of adults simultaneously jumping next to a seismograph will quite visibly move the needle.

A decent explosion will register as 1.0 ~ 2.0 about 25 miles away, to judge from the bombing tests they used to do at the naval airbase by where I grew up, and the time-matched jumps on the lighthouse graph. Be warned that 1-2 richter quakes are REALLY common. To bump it up to visible levels? Like, say, 3-4? You'd really need to suddenly demolish the building, assuming you're relying on Council Island noticing - especially since Lake Washington won't transfer the shockwave nearly as well as rock.

Though if you demolish the building, the S-S on Council Island will probably just SEE it blow up.

It's extra-territorial land, so I imagine the S-S will know, but they will just accept what happened at the Azzie facility as their own responsibility. The Azzies would probably assign a team to forensically investigate the explosion. ANd they'll try and trace it by the chemicals in the explosion, in combination with whatever they may have gotten from salvageable security records and whatever other surveillance they had (eg. sattelite). If the runners covered their tails well enough, the trail will likely go cold.

You can hear explosions a long way away. And the column of black smoke from the fires would be visible for 10-50 miles away.

I never cared for physics compared to biology, but wouldn't water carry the shock far more efficiently then rock?

Having lived in a mining town, and feeling the effects of blasting all the time through much weaker explosives, I'd have to say taking out a building like that isn't going to be felt for very far.

For the first part, it was probably an implosion rather than explosion (The building collapsed in on itself, which is how they take down buildings IRL), which means that the effect is designed to fall in upon itself, rather than radiate out (Like, say, you're blasting a Tunnel in a Mine, which is shaped outwards and will radiate.).

Seismically, unless they screwed up the Demolition Roll (Which also would mean the building wouldn't come down), it'll be a "Non-Event" for any stations that aren't in the IMMEDIATE area. (As in, coughing up dust from the building.).

Now, that's conventional explosives and feeling it. It'd have to be underground, and shaped outwards to feel at any real distance.

The S-S would probably investigate the dust cloud that rose up. Maybe, if they don't have better things to do (Like police Smugglers, keeping the Cascade Orks in line YET AGAIN, and so on.).

They'd probably send a small recon unit (Platoon Strength or a Fire Unit if heavily tasked at the moment) out, they'd see it was Azzie territory, laugh their hoops off, and go away, sight unseen. Unless they see the the 'Runners on their territory, then they'd have to "Go forth and offer assistance to the Aztechnology Survivors of the Accident Site" and, well... There you go. The next adventure hook!

Magic Items going "Snap", that would be a GM's call. How powerful are they, were there any spirits close, did they survive the thaumaturgical backlash, and so on.

Nope. The denser the substance, the faster a shock wave travels through it. Water works better than air. Rock works better than water.

They just seriously pissed off one of the meanest, nastiest, most ruthless corps in SR and you're worried about how a big a "BOOM!" it makes in a Richter Scale? I would think that how big a "BOOM!" the PGM makes when it impacts with their conapt would be the real question of the day...