When you said Seattle and described the sound I immediately thought "F/A-18s out of Whidbey".

We hear sonic booms irregularly on Lake Huron from fighters heading between the training ground up north and Selfridge AFB. Over land they're rare but over open water they like to light it up.

Strange they had to scramble all the way from Oregon.
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Safety is something that happens between your ears, not something you hold in your hands.
- Jeff Cooper