Ancient Fault Lines in Pennsylvania

Older buildings on the East Coast are vulnerable to earthquakes in the region.
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When you hear about earthquakes in the United States, your first thought might be of California. However, it may surprise you to know there are ancient fault lines like the Ramapo fault and Ramapo seismic zone in Pennsylvania, which are active. The United States Geological Survey keeps records of all earthquakes that occur, not just in the west of the country but in the east as well. The Ramapo fault extends from New York through New Jersey into southeastern Pennsylvania.

Earthquake Magnitude Scale

To understand the damage an earthquake can cause based on its seismic magnitude, Michigan Tech University created the following list of magnitude ranges and their effects:

  • 2.5 or smaller earthquakes – most people don't feel these and they generally cause no damage
  • 2.5 to 5.4 earthquakes – most people can feel these, but they only cause minimal damage
  • 5.5 to 6.0 earthquakes – cause slight damage to buildings and structures, based on building's construction
  • 6.1 to 6.9 earthquakes – can cause much damage in populated areas
  • 7.0 to 7.9 earthquakes – represents major earthquakes that result in severe damage
  • 8.0 or greater earthquakes – can destroy cities or communities near their epicenters

East Coast Fault Line Earthquakes

Most of the earthquakes on the East Coast fall below a 4.0 magnitude, which is a measurement of the seismic amplitude of an earthquake and its strength – but in 1884, an earthquake registering 5.2 occurred near the Ramapo fault line, destroying chimneys in New York, while people as far south as Virginia and north to the state of Maine felt the shaker. Several other earthquakes ranging from 2.0 to 4.5 have hit the East Coast up to the present time with little to no damage. But buildings in this region, many of which are historical in nature or made of brick, could suffer or experience damage because of another mid-range earthquake.

Longest Fault Lines in the U.S.

At over 800 miles ling, the San Andreas fault is the longest fault line in the United States and is responsible for the massive earthquake that decimated San Francisco on April 18, 1906. This fault extends from Southern California to off the Northern California coast just beyond San Francisco, getting its name primarily from its northern branch. The San Andreas fault marks a transform boundary between the North American and Pacific tectonic plates.

The Cascadia subduction zone, the second longest fault line in the U.S., connects to the San Andreas fault line via the Mendocino triple junction fracture zone off the Northern California coast and runs north 680 miles off the coasts of Oregon and Washington up to British Columbia. Geologists predict that an earthquake along this fault could devastate Portland, Seattle and Vancouver.

Scientists indicate that the Cascadia fault is similar in scope to the fault off the coast of Chile in South America that has resulted in several high-magnitude earthquakes of long duration. They predict that a Cascadia earthquake could last 4 minutes at a magnitude of 9.0 or greater. Geologists also expect a tsunami to hit regions of the Pacific Northwest extending from the Northern California coast along the coasts of Oregon and Washington 20 to 30 minutes after the earthquake.

The New Madrid Seismic Zone, one of the most active faults in the nation outside of the west and more active than the New York fault line and the PA earthquake fault line, is located in the U.S. heartland. It runs from southeastern Missouri through northeastern Arkansas to western Tennessee, western Kentucky and southern Illinois. In 1811, it shook the area with an earthquake of 7.5 with over 2,000 aftershocks experienced over five months after the earthquake.

The fourth largest fault zone, the Ramapo seismic zone, starts in southeastern New York and extends into southeastern Pennsylvania with branches into New Jersey. The U.S. Geological Survey site shows the Ramapo seismic zone as currently being active with many mini earthquakes, usually ranging below 1 up to 4.5. The Ramapo fault zone is not the only earthquake-prone area in Pennsylvania, as an active PA earthquake fault line in Erie, Pennsylvania, was responsible for the 5.2 earthquake that shook the region in 1998.

The Ring of Fire

At least 90 percent of all earthquake activity in the world occurs along the continents that border the Pacific Ocean, nicknamed the Ring of Fire. This area also serves as home to 75 percent of the world's volcanoes. The world's largest exposed fault line called the Banda Detachment – recently discovered along the Ring of Fire off the coast of eastern Indonesia in the Banda Sea on the Ring of Fire – exposes a fault plane on the sea floor that covers over 23,000 square miles and runs just over 4 miles deep.

Types of Earthquake Faults

A fault line occurs where tectonic plates or boundaries meet. With three geological boundary types – divergent, transform and convergent – three basic types of faults define the activity that occurs where these boundaries meet. These faults include the strike-slip fault typically found along transform boundaries in which both plates slide horizontally, normal faults occur along divergent boundaries where one side of the boundary drops below another, and the thrust fault where one side thrusts up instead of down. Many earthquakes zones include faults that consist of combinations of these fault types like the San Andreas fault zone that is 95 percent strike-slip and 5 percent reverse or thrust fault.

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