Eavesdropping on Earth
Life comes with a soundtrack on Aubrey MacDougall’s and Laura Johnston’s dairy farm in Ormstown, Que.: There is the steady whir of the ventilation fans, the pulsing swoosh of the milkers and, of course, the occasional moo. But from one corner of the 93-acre property, scientists are remotely tuning in to the subtle rumblings of the planet beneath.
Since 2013, the farm has hosted a small seismic station designed to pick up minute vibrations from earthquakes taking place all around the globe. It is sensitive enough to have easily registered the 4.8 temblor that shook Michigan over the weekend as well as the devastating 7.8 Nepal earthquake of April 25 – an event half a world away.
The station is one of hundreds deployed in a giant array that currently stretches from the St. Lawrence Valley to Virginia. The array’s purpose is not simply to detect earthquakes but to use them to visualize what is happening below the surface. Since earthquake vibrations are affected by changes in the composition and density of the material they travel through, it’s possible to combine data from many stations to map the three-dimensional structure of solid rock.
For more than a decade, scientists have deployed a band of seismic stations in a grid-like pattern to build up a three-dimensional image of the geologic features that underlie much of North America. The stations have been moved from west to east and are now deployed in the Northeastern states, Ontario and Quebec. (Murat Yukselir/The Globe and Mail) Source: Andy Frassetto/Incorporated Research Institutions for Seismology
“The end result is really a clear and uniform picture of what’s under the continent,” says Bob Woodward, who heads the Washington-based USArray as part of a broader effort known as EarthScope. Ultimately, scientists hope the picture will allow them to figure out how North America was assembled over the course of geologic time.
“We just thought it was really cool,” says Ms. Johnston, who adds that she and her husband were happy to have a seismic station placed on their land after other property owners in the area declined. “Why not participate if we could?”
May 6, 2015