If the ground moves and no one feels it, is it still a big deal?

The ground has been moving under your feet for the last few weeks, and you probably didn’t even notice. A series of micro quakes have been bubbling 20-miles below the surface, and seismologists aren’t sure why or what it means.

Scientists have been studying these long-lasting but small tremors for about a decade. It’s only been that long that they even knew they existed.

John Vidale is director of the Pacific Northwest Seismic Network and the Washington State seismologist. He said they are like an earthquake in slow motion. When taken in total, they pack the same punch as a major earthquake, like a 7-pointer.

“The total motion is enough that we’d feel it if it happened in a few seconds like an earthquake, but when it takes that long there’s nothing much to feel up here,” he said.

These tremors have been consistent since they were detected. They happen about every 14 months. They usually move from south to north, from about Tacoma up through Vancouver Island in British Columbia, kind of like a zipper opening along the fault.

But this year, Vidale said, the pattern is different. “This last time instead of starting in Tacoma the event started under Vancouver Island,” he said. “Instead of lasting as long as it usually did, it’s lasting longer and spreading across a bigger patch that usual.”

The scientists don’t know what it means. They only have ten years of data so they aren’t sure if this is normal or unusual.

“It’s a little bit frustrating,” Vidale said. “We’re seeing in ever greater detail how they move in lots of funny patterns that we didn’t expect, but what’s actually causing the motion we’re still trying to figure out. We know it’s due to the plate tectonics, the two plates around here moving a couple of inches a year relative to each other, but why it takes a month instead of a minute for this motion to happen is still a mystery to us.”

What Vidale is hoping is that studying and understanding these long-lasting but small events can help them predict when bigger earthquakes will hit, but he’s not sure that will ever happen.

“It might be that no matter how carefully we look all we can see are hints of slightly increased danger before something happens,” he said. “We’re optimists. We’re always looking for something that will give us a lead, but we just don’t know how powerful these methods might eventually be or how useless they might be.”

What he does know is that the ground is moving about an inch in one direction or the other every year. It’s happening beneath our feet all the time, and we’re clueless.

I guess that’s better than having fast-moving, big quakes, that we do feel.