Over the past week, our planet has experienced a series of significant earthquakes. The world’s sixth-strongest recorded earthquake shook off the east coast of Russia, registering as an 8.8. While several earthquakes, like this one, take place on the boundary of Earth’s major plates, today’s focus is on those who break the norm and shake the planet away from major hotbeds.

Between August 6th and August 8th, two earthquakes struck the New York metropolitan area, far from any seismic hotspots. While very uncommon, earthquakes on the U.S. East Coast can come from very different reasons, and actually have far worse impacts on our lives. Let’s first understand how earthquakes happen.

 

 

The top layer of Earth’s structure is called the crust. It is a thin layer that contains the land we live on and the oceans we swim in. The crust is not in one piece, though, as it is split up into different fragments, or plates. These plates can range in size from continental to tiny. These plates move in different directions over long timescales. For example, two plates generally separate the Pacific coast of the U.S. and the Pacific Ocean- they are moving parallel to each other. When these plates move, the rocks catch on with each other and slowly build up energy. Slowly, more tension is put on these rocks until the amount of stress overpowers the rock’s tangled structure, and it finally fails. Once this happens, a massive amount of energy is released and pulsates up to the surface.

 

 

This activity is common across faults, or the boundary between two plates. A classic example of a fault is the San Andreas fault in California, made infamous by earthquakes impacting San Francisco in 1906 and 1989. There are no active faults in our area, as the entire Valley lies in the middle of the North American Plate. This is just one difference between how earthquakes can impact the eastern half of the country.

 

 

 

The rock underlying the Valley is quite old. So old that it is unusually hard and dense compared to rock beneath the Rocky Mountains and the Pacific Coast. When earthquakes occur, they rely on hard, dense rocks in order for seismic waves to go through them efficiently. Earthquakes travelling over faults, as is commonplace on the West Coast, is another way to limit the distance for waves to travel. With this being said, tremors can travel much further distances across the East as compared to the West.

 

 

This can be proven by comparing two similar-sized earthquakes across coasts. A magnitude 6.0 earthquake, which impacted California’s Bay Area in 2004, occurred along an active fault line and was felt across the middle third of the state, stretching to the Sierra Nevada Mountains to the east. Compare this with a 2011 5.8 earthquake over Central Virginia, where people felt the quake all across the Mid-Atlantic, Northeast, and Southern Canada- the Valley included.

 

 

Owing to the fact that East Coast earthquakes are rare, buildings are not made to withstand strong enough tremors. For this reason, impacts from surprise quakes can pile up quickly. In the case of the 2011 earthquake, over $200 million in losses were reported, and D.C.’s Washington Monument had to be closed for multiple years due to structural damage.

The original question, however, still needs to be answered- how do earthquakes form in the middle of a continental plate? While activity largely occurs on active faults, there are tons of inactive faults across the eastern half of our country. Millions of years ago, our region used to be a hotbed for seismic activity. However, faults are antiquated and are underneath the ground today. While not actively moving, other factors could stir up these faults and cause low-scale quakes. The Earth’s crust is still recovering from glacial melt from the last ice age, officially coined “glacial rebound”. This causes the crust to move upwards and potentially causes stress on ancient fault lines. Additionally, movement from other plates could bleed some stress further into the plate, causing small bouts of tension that can get relieved by interior faults.

More recently, some earthquakes have been blamed on human-spurred causes. An earthquake had never been recorded in Youngstown until 109 earthquakes occurred in 2011 alone, just after the opening of the Northstar 1 deep injection well. On December 31st, 2011, the area was shaken by a magnitude 4.0 earthquake, prompting the closure and abandonment of the site.

 

 

While no seismic activity is expected for our area, be sure to download the Stormtracker 21 app for all of the Valley’s weather-related updates.