In last week's post (https://www.usgs.gov/observatories/calvo/news/mystery-noon-booms-part-1), we challenged you to give us your best hypotheses as to what was causing the 'Noon Booms' CalVO seismometers were picking up.
The Mystery of the Noon Booms Part 2
There were some great ideas (heat effects, sonic booms, mining operations) and some less plausible ones (aliens), but in the end a few of you came up with the same conclusion as our seismologists. (Drum roll...)
If you guessed munitions detonation at Hawthorne Army Depot, you're bang on!
According to our seismologists, the signals picked up by our seismometers are consistent with an explosive source located near the Hawthorne Army Depot. These seismograms show Noon Booms on instruments in the Clear Lake Volcanic Field from June 26, 2023 as well as an older example from Long Valley on March 11, 2020. The instruments are ordered by distance from the depot, with dashed lines that follow the speed of sound in air (343 m/s or 767 mph). Atmospheric effects (such as wind direction) affect where we see these signals, which is likely why we didn't see last week's boom on the much closer Long Valley seismometers.
The Hawthorne Army Depot is actually located in Nevada about 50 miles north of the Long Valley Caldera. According to their website, they "store conventional munitions, demilitarizes and disposes of unserviceable, obsolete, and surplus munitions". An example of one of the controlled detonations can be seen in this video at 1:38: https://youtu.be/6Zhjkh_KA7c?t=98
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