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How The Greenwood Explosion Created a Pressure Wave

Cliff Mass discovered that the shockwave from the Greenwood explosion could be felt all around.

Early Wednesday morning, a natural gas leak explosion leveled two buildings and damaged three dozen surrounding businesses in the vicinity of 85th Street and Greenwood Avenue in Greenwood. Nine firefighters were also injured in the blaze. It will likely takes weeks to determine what why there was a leak but we know that the damage has been approximated at $3 million and means tough times ahead for the owners of Neptune Coffee, Mr. Gyros, and Greenwood Quick Stop.

Speaking of the way the blast affected those around it, Cliff Mass had a feeling that the explosion must have created a powerful pressure wave (shockwave), not just in the immediate area but throughout Seattle. He did some digging around and discovered that it was true.

But then I got a message from Professor Steve Malone of UW's Earth and Space Sciences Department. Steve is an expert in seismology and it turns out that many seismographs are paired with very accurate barometers. Eureka! A number of his microbarographs recorded the pressure signal, even ones 10s of kilometers away. Here is a sample from a unit about 50 km distant from the explosion. A pulse of roughly .17 Pascals (Pa) around 0948 UTC (1:48 AM), with some aftershocks/vibrations for about a minute after.

That's still relatively small as far as pressure waves go, though it did create aftershocks for the next minute or so. While it would have been extremely loud to those in Greenwood, it would have likely been just part of the noise pollution in surrounding neighborhoods.
· Huge Gas Explosion Creates Pressure Wave over the Northwest PLUS a Powerful Storm Hits Our Coast [CM]
· Seattle explosion leaves heart of Greenwood neighborhood a gigantic mess [ST]