Skyquakes.
There’s speculation on the cause of them and exactly what they are. Videos of them were out long before AI became mainstream like it is now, but back 10+ years ago people still claimed much of it was just edited and fake. I came across the term after I personally heard an odd deep sound one night when I was driving outside of the populated cities.
The sun has supposedly had some high activity recently, and some people speculate that coronal ejections, or energy expelled from the sun - could be an explanation for them. The Aurora Borealis or “Northern Lights” are brought to us by the activity of our Sun.
I’m actually fascinated by odd noises like this. I’ve always loved Thunder storms, and would be happy in Tennessee just sitting on the porch at night watching a storm in the distance with the warm summer rain coming down. Without researching this incident, perhaps its source has been found.
Meteors can be an explanation for spontaneous booms like an explosion, but often times are observed widely and well reported. I’m not sure the audible range of a meteor breaking atmosphere, and Ive never heard one myself.
People speculate potential sounds caused by humanity. Sonic booms, which are federally mandated to be illegal. But perhaps sometimes you gotta do what you gotta do. It’s not that pilots are not legally allowed to break the sound barrier, but that it’s illegal to do so basically “within city limits”. Military can get special permission to break this law. It’s something which is currently regulated and also up for debate with the potential that we could see changes to this law in the future.
Due to our close proximity to the coast (considering the speed of travel) I don’t think it’s illogical that Portland would be in that area potentially affected by a sonic boom from any aircraft traveling towards the Pacific. Breaking the sound barrier would produce a loud sound which would sound like an explosion coming from the sky.