Earthquake rattles Ridgefield residents

Ridgefield residents woke Wednesday morning feeling a bit rattled.

That’s because a  magnitude 2.2 earthquake was registered in the Lake Mohegan area of New York — west of Goldens Bridge — at 6:14 a.m., according to the U.S. Geological Survey.

Several residents posted on social media about the quake.

“Rattled windows in Ridgebury,” said one resident on Facebook, “deep rumble.”

“Things fell in my kids’ rooms above me,” added another resident, who lives near Rainbow Lake.

"This is something for us all to think about: The epicenter of this 2.2 quake is 20 miles (as the crow flies) from town hall," another resident posted. "But it is only 8 miles from the Indian Point power plant. If the energy we felt dissipates at something like the square of the distance (physicist please correct me on this), then the effect of the quake as measured at Indian point would be something like 6x the effect felt in Ridgefield."

There were no immediate reports of injuries or damage.

West Lane residents — and some others in the downtown area — also reported feeling the quake.

Lake Mohegan is about 50 miles north of New York City.

Ridgefield has experienced quakes in the past because it lies on “Cameron’s Line,” a fault that runs from Manhattan northeasterly through Westchester and into Ridgefield. The last earthquake that was felt in town was Oct. 19, 1985.

History of Cameron's Line

At 6:07 on the morning of Oct. 19, 1985, Ridgefielders who were awake—and those who were awakened—felt something unusual. Their homes were shaking: dishes rattled a bit; pictures tilted a tad; old plaster may even have cracked. They were experiencing the effects of the first significant earthquake in the New York metropolitan area in a century.

Centered near Ardsley, N.Y., in neighboring Westchester County, the quake registered 4.0 on the Richter scale. The previous major earthquake, in 1884, measured 5.0. There was no significant damage in Ridgefield and little elsewhere, though a New York town reported some cracked pavement.

However, the quake brought to light a geological phenomenon that had been little known outside scientific circles, and that affects the very foundation, literally, of Ridgefield. The quake was strongly felt along “Cameron’s Line,” a fault that runs from Manhattan northeasterly through Westchester and into Ridgefield. Here, the line enters near the southwest corner of town and almost exactly follows West Lane and High Ridge into the village. It continues across Prospect Ridge, through Great Swamp and Farmingville, then into Redding, on up to Danbury and northerly into Litchfield County.

But Cameron’s Line is no run-of-the-mill fault. As veteran science reporter Walter Sullivan explained it in The New York Times the day after the quake, the line “marks an abrupt change in the earth’s crust that resulted from a collision between North America and a European-African land mass 400 million years ago.”  Later, the European-African continent pulled away, leaving behind a piece of its edge.

Geologists with the Hudson Institute of Mineralogy describe the result this way: “The rocks south of the Cameron’s Line are mostly Ordovician unnamed felsic orthogneiss with some of the Harrison Gneiss metadiorite in the Branchville area. North of Cameron’s Line, higher elevations with rugged topography along the eastern, northern and western part of town (such as under Pine, Ned, and West Mountains), are underlain by Grenville age Laurentian gneiss bedrock.”

More simply put, if you live in the southern third of town, the earth beneath you closely matches the geology of today’s western Africa while folks in the northern two-thirds of the town live atop North American rock.

Mild quakes, the kind most people would not even feel, occur fairly often along Cameron’s Line and many other faults in the region. The 1985 quake in Ardsley was actually centered two miles west of the line, but it was felt along the fault on up into western Massachusetts. Connecticut as a state has several earthquakes a year, but they are below 2.5 on the Richter scale, and generally not felt. The area around Moodus, in eastern Connecticut, is famed for its “rumblings” and has experienced series of up to 400 quakes over six weeks, mostly too small to feel. (Native Indians called East Haddam, the next town south, morehemoodus, “place of noises.”)

In October 1989, the Loma Prieta earthquake in California registered 6.9, killed 63 people, injured 3,700, and damaged 12,000 homes and 2,600 businesses. Forty buildings collapsed in Santa Cruz. A week later, scientists told The Ridgefield Press that the town could experience an earthquake “with the level of violence and…havoc” of the California quake. Here, however, the damage would be even worse than an equivalent shock in California, both because most buildings haven’t been designed with quakes in mind, and because the crust of the earth is more solid and able to transmit and maintain the magnitude of earthquake waves than the softer ground of the West Coast.

That same year, the state passed building codes incorporating the need for seismic designs, but many older buildings—such as most of our schools and the Town Hall—are brittle brick and/or cement block structures that don’t do well in quakes (wooden houses are the safest).

There are many faults that crisscross the metropolitan New York region, and scientists seem uncertain about the level of danger they may present. The faults are certainly not as active as California’s. Back in 1985, Columbia University seismologists said the Oct. 19 quake might have been a warning of a more severe quake to come within months. “They stressed, however, that this was a possibility, rather than a probability, and other specialists expressed doubts regarding the prognosis,” said The Times.

In 2011, the 5.8 quake in Virginia that damaged the Washington Monument was felt in Ridgefield (and across 12 states and southern Canada). But as of this writing, no local quakes like Arsley’s has occurred since 1985. And for most of us, that’s just fine. —from Hidden History of Ridgefield, © 2015, The History Press.