If you didn't feel the big East Coast earthquake of August 2011, you may have felt some of the smaller tremors that have occurred in New Jersey during the past five years. Watch video
Buildings swayed, windows shook, and nerves were rattled.
Five years ago today, one of the largest earthquakes ever recorded in the eastern United States rocked a rural area of Virginia, sending shock waves through the ground across much of the East Coast, into New Jersey and as far away as Canada.
The Aug. 23, 2011, earthquake, which had a magnitude of 5.8 on the Richter scale -- a strength that's rarely seen in the eastern U.S. -- caused millions of dollars in structural damage to homes, schools and businesses in Virginia. It also damaged structures in Maryland and in Washington, D.C., including the Washington Monument.
In New Jersey, no major structural damage was reported, but residents across the state felt the ground shaking, and some buildings were evacuated.
"I was sitting here in my office, and my desk started to move," Richard Dalton, a geologist at the New Jersey Geological and Water Survey in Trenton, recalled. "My wife was driving to the bank and she thought something happened to her car because her car was shaking."
Since that quake, New Jersey has had 29 earthquakes, including 12 this year, according to data from the U.S. Geological Survey, the federal agency that monitors seismic activity across the world. All of New Jersey's quakes, however, have been far smaller than the Virginia earthquake -- and many have been so small that no resident reported feeling any shaking or hearing any rumbling.
Those small tremors are the most typical types of earthquakes to occur in the Garden State, said Robert Williams, a geophysisist at the U.S. Geological Survey. The vast majority of earthquakes detected in New Jersey have a magnitude of below 1.0 on the Richter scale.
"People are not going to feel 1.0's and maybe even 1.5's," Williams said. "Generally when they are above two or two and a half in the East, people will feel it."
That's exactly what happened in August 2011, and it's also what occurred last summer, when a small earthquake centered near Bernardsville rattled homes in Somerset and Morris counties. It turned out to measure 2.6 on the Richter scale, the largest tremor detected in New Jersey in recent years.
Another recent tremor that got noticed was a 2.1 magnitude quake centered in Ringwood in Passaic County on Jan. 2, 2016, shaking houses while people were sleeping.
No reason for alarm
Although there have been 12 small quakes detected in New Jersey so far this year, far more than the four that were detected last year, experts say there's no reason to be alarmed. Dalton said it's likely the uptick is the result of the recent expansion of earthquake detection sensors throughout the region and modern digitalized equipment that can pick up even the slightest movement in the earth's bedrock.
Much of New Jersey's seismic activity during recent decades has been concentrated near the Ramapo fault system, which extends diagonally from southern New York state down through northern New Jersey -- in parts of Bergen, Passaic, Morris, Somerset and Hunterdon counties -- and into eastern Pennsylvania. Another active area for minor tremors, Dalton said, is the New Jersey Highlands in the northern and western region of the state.
All of those green dots on this map are places where people felt the ground or buildings shake during the big earthquake that was centered in Virginia on Aug. 23, 2011. (U.S. Geological Survey) Faults are cracks in the earth's crust, and earthquakes occur when there is a sudden slip, or displacement, of rocks on a fault. The U.S. Geological Survey says earthquakes release energy in waves that travel through the earth's crust, causing the shaking that is felt by people near the epicenter and sometimes by those who are many miles away.
In fact, earthquakes that occur in the eastern United States tend to be felt by more people than those that strike out West, even if the quakes are the same magnitude, Dalton said. The shock waves travel further in this region of the country, because "our faults are very tight" and faults in the western United States are more fractured.
The tighter the faults are, the longer the shock waves will travel, Dalton said, which is why the Virginia earthquake in August 2011 was felt hundreds of miles away in New Jersey, even further north in New England and northeastern Canada, and as far west as the Mississippi River.
Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com. Follow him on Twitter @LensReality or like him on Facebook. Find NJ.com on Facebook.