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Hilltown Archives — The Altamont Enterprise, August 25, 2011

Knox Rocks
As nation reels from Virginia quake, Hilltowns feel their own tremors

By Anne Hayden

HILLTOWNS — People up and down the East Coast Tuesday felt the tremors from an earthquake in Virginia, but they didn’t feel the two small quakes that shook the Hilltowns.

According to Dr. Chuck Ver Straeten, New York State Museum and State Geological Survey geologist, the first two earthquakes recorded in Knox since the 1970s occurred on Monday evening and Tuesday morning.

At 7:15 p.m. on Monday, an earthquake with a magnitude of 1.9 was recorded at a depth of 10 feet; at 6:35 a.m. on Tuesday, a quake with a magnitude of 2.2 was recorded at a depth of 13.3 feet.

The epicenter of both quakes was less than one mile northeast of the hamlet of Knox.

“The epicenter is the point at the center of the earth above where the quake happens,” explained Ver Straeten. He said both quakes were too small to be felt.

“I spoke to someone who lives less than a mile from where the earthquake happened on Tuesday, and she said she didn’t feel anything,” he said.

Neither of the earthquakes in the Hilltowns had any relation to the bigger quake that occurred around 1:50 p.m. in Virginia on Tuesday.

“There would be no relation across that type of distance; if there was a foreshock, it would only occur within a radius of tens of miles of the major incident,” Ver Straeten said. On Tuesday alone, there were four earthquakes in Virginia; one in Washington; one in Oklahoma; two in Hawaii; three in Colorado; 22 in Alaska; and 26 in California.

The reason that the earthquake in Virginia was felt so far up the East Coast has to do with the way the mountains were formed millions of years ago. When mountain building occurs, the rocks heat up, but then, over time, they cool down and become rigid. The tremors of an earthquake will travel farther when rocks are rigid, according to Ver Straeten.

The Virginia quake was likely caused by rocks sliding along a major fault line, and Ver Straeten said the Knox quakes could have a similar cause.

The East Coast was a site of major mountain-building activity between 250 million and 1.2 billion years ago, and some of the faults from that time are still deep in the rocks. Exposed rocks containing faults in the Adirondacks run under the ground to Albany, and most likely to Berne, he said.

Ver Straeten has been looking at places in the Helderbergs and has found some very small faults, or layers in the rocks that have dropped about 40 centimeters, and are uneven. However, he said, there is no way to know when the drops occurred.

“Obviously there are faults deep under the Helderbergs, though, as evidenced by the earthquakes here,” he said. From February 2009 to March 2010, there were 38 earthquakes recorded in Berne.

“From March 2010 to now, things were completely quiet, and that’s just the way it is,” said Ver Straeten.

There is no cause for concern over the quakes in the Hilltowns, he said. A number of minor earthquakes, despite the cause, is a good thing, Ver Straeten said. Movement along a fault generates activity, and, when lots of tension builds up with no release, large movement can occur, triggering a major earthquake.  The small, frequent temblors in the Hilltowns indicate minor slips along fault lines, which means there is less chance of a tension build-up and a major earthquake.

There have only been five earthquakes in New York State over a magnitude of five since 1884. The last one was in 2002, outside of Plattsburgh, and had a magnitude of 5.1; the biggest one occurred in 1944, along the Canadian border, with a magnitude of 5.8.

There is no ability to predict when earthquakes will happen, Ver Straeten said, but certain gases do tend to start escaping along fault lines when activity occurs, so if the gas can be measured, it might serve as a precursor.

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