Estimated read time: 2-3 minutes
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Ed Yeates Reporting"It was like a semi truck driving by and hitting a pothole. And there was one loud impact. You couldn't hear it, but you could feel it."
As earthquakes go, last night's shaker was nothing to shout about. In fact, if it had happened outside the Salt Lake valley, nobody, probably, would have felt it. But it happened here, and where it happened and what caused it are worth talking about.
9000 south and the Jordan Bottoms is the epicenter, where it kicked off seven to eight miles below the surface. Right under the valley floor, that's about where our infamous Wasatch Fault ends up.
In areas where it's clearly mapped, the fault runs on an incline down to a depth of about ten miles. But this was a small tremor, not what you'd expect from the big boy. Our really big Wasatch fault moves vertically, but last night's shaker occurred on a little horizontal fault.
Jim Pechmann, University of Utah Seismograph Stations: "The sense of motion in this earthquake is similar to the sense of motion that occurs on the San Andreas fault."
The San Andreas Fault in California, that is, but on a much smaller scale. Seismologist Jim Pechmann with the University of Utah Seismograph Stations says there are lots of these small faults out and about in our valley. Last night, one of them creaked a bit.
Stacie Fuller: "I was in the recliner and it rocked. So I freak out and my husband just sits there and like, it's nothing."
Blaine Anderson: "We heard a popping. Then we heard a rumbling and the computer was rocking around on the desk."
The folks who felt this at the epicenter probably got just a taste of how little ground motion it takes sometimes to rock, like Jell-o, the deep unconsolidated silts and sands that make up our old lake bottom.
Jim Pechmann: "For a small earthquake like this, I would expect ground motion on deep soil sites to be amplified relative to ground motion at rock sites."
In 1992, there was a 4.2 magnitude quake about eight miles southwest of there. A lot of people in our Salt Lake valley bowl of jelly felt that one.
So, is this a precursor to 'The Big One?' Experts say there is a one in twenty chance that this is a precursor to something bigger, but that ratio is based on anything bigger than a 2.1. So it could be a 2.2 or 2.3, nothing to worry about.
