Extreemly Loud and Long Sonic BoomHello, I was sitting in my ground level apartment this morning at approximately 11 am when I hear a sonic boom. I've lived near airports before so I've heard sonic booms before, but this one was unusually loud and long. It last approximately 13 seconds, and was done so close to the ground that I could feel it though my wheeled chair. It’s very unusual for us to have sonic booms where I live, although the Salem airport does have military vehicles, and aircraft, it is located almost directly south from my apartment.The boom had an odd characteristic, I don't know if it’s from how close to the ground it was, but there seemed to be a low level rumble that preceded it by a second or two followed by the usual explosion of sound a boom creates. From how it sounded it was going from south to north, and as I said it took nearly 13 seconds for the boom to begin to fade. Unfortunately, I wasn't dressed well enough to step outside to see what created the sound, but I can safely say I've never heard a boom happen like that before. I'm lived in the apartment I'm in for 4 years, and lived around airports most of my life. I lived near the Salem airport for 7 nearing 8 years, PDX the Portland International Airport for 10 years, and 10 years due west of the Hillsboro airport where the Blue Angels flew overhead during the airshow all 10 years I lived there. I’m no military expert, let me say that out front. I’ve worked in customer service most of my life, but have seen several different military vehicles living near the airports I’ve lived in, and while I couldn’t ID them, I am familiar with the booms they make. I’ve never heard one quite like what I heard today between the preceding rumble, the odd vibration to the boom, or the feeling of the chair under me vibrating slightly from it. Hope this helps with all future ventures in to investigations.