People still have fireworks left over from last weekend. Isn't that most likely?

I heard it near 43rd Ave E and it sounded like it was very close, but it may not have actually been. It echoed around the neighborhood in a strange way. I figured maybe a firecracker gone wrong or something?

Lindap's sewer line?

Anyone lose power ... or a squirrel. When those trash can sized electrical transformers get shorted out and blow it sounds like the earth is opening up.

Sonic boom from one of the 148th out playing over the lake?

There were two huge explosions today around 1 p.m.  Could've been sonic, they were really loud, but still sounded somewhat distant from Lakeside/Catholic Church area.  Tall ships firing cannon at civilians?  Or maybe it was Meteor shit?

My money is on Tall Ships firing for a demo.