I spotted a small local earthquake signature on the helicorder of my Shake and Boom this morning. I checked the next closest Shake (6kms away) it was there too, and then checked the next closest but the signal was not obvious at all. That’s unusual… it’s obviously small… so I ran my localstations.py code to work out where it was.
Only having a good signal at two locations wasn’t good, so I took and educated guess that the location would be Oberon Quarries - not far away. The result of the section plot:
I decided to ring the quarry to confirm they did a blast. After they put some effort into comforting me that it wasn’t an earthquake, I told them I had a seismograph and could see by the signal it wasn’t an earthquake, and explained I just wanted to confirm my observation. That relaxed them a bit ;o) and before I knew it, I’ve been invited to go up and get inducted so I can push the button on a blast! I’m happy with that! lol!
The spectrograms and FFT plots on the signals show strong spikes at about 24Hz and 48Hz which correspond to detonation intervals of 0.042s and 0.021s.
I tend to use the Displacement section plot to estimate the magnitude as the errors involved are less with displacement and the section plot averages the M calcs across all the stations.
The infrasound plots are interesting because you can see the infrasound from the seismic waves arriving before the direct infrasound wave. The delay from the Seismic arrivals to the start of the infrasound should allow a calculation to be made of the distance where the seismic waves stopped producing infrasound strong enough to reach the station.
The direct infrasound arrivals also show on the seismic signal at about +13s for R21C0 and +29s for R5968.
It was interesting talking to the quarry manager (I rang again to confirm the blast as I don’t have good triangulation). He was saying they used det cord this time instead of electronic detonators, so the detonation interval has more variation in it, and the blast should sound louder (compare the peak dB for the two blasts!).
