The USGS came in late last week using their latest ground radar and found that there were some quakes earlier in the week that could have explained it. The mayor and them were cautiously optimistic but alas the booms are intensifying again.
One thing is for sure the Town is benefiting by all the attention so maybe it's the whole town's prank?....lol
Consider, propane is 1.5x denser than air. So, find an underground sewer - run a hose down a pipe to the sewer and let the propane tank run for 45 seconds. Wait another 30 seconds for the fumes to settle, then drop a firecracker down the pipe.
Nice deep underground ‘Boom’. Cheap, probably repeatable, loads of fun.
I grew up in California, lived there for most of my life, and been through MANY earthquakes. I do not recall any booming sounds through any of them. Granted, I know that all earthquakes have different characteristics. Again, been through different types. The rolling action. The jolting, jarring action of some of them. Never any booming involved.