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Epicenter
Epicenter of the Earthquake was
in Mineral, Virginia, 450 miles
from Albany, New York.

How an Earthquake in Virginia Shook up New York State

Why do some localities feel earthquakes more than others?
Throughout New York State, residents experienced the shaking of the ground as a result of the strong earthquake whose epicenter was over 450 miles away in Virginia. However, other locations experienced very little to no shaking at all. How is this possible? The explanation for this largely has to due with the distribution of glacial deposits, specifically lake sediments such as clay, and a process known as seismic wave amplification.

Seismic Wave Amplification
When an earthquake occurs waves of seismic energy are released into the
ground in the form of compressional waves, shear waves, and surface waves
(USGS Link of Seismic Waves).  As these seismic waves travel through the Earth, the speed of these waves is affected by the different materials encountered.  Generally the shear wave component of seismic waves will travel faster in harder materials like rock and gravel and slower in soft materials like clay. Borcherdt et al. (1978) used information from the 1906 San Francisco earthquake to link shear wave velocity to soil or rock type and ultimately to wave amplification.  Wave amplification occurs as the shear wave slows in a soft material like clay. The wave energy is transferred to the soft clay thus causing a significant increase in movement of the ground.  This amplification of wave energy can result in greater shaking of the ground which allows the seismic energy to be felt more readily in some areas and can also increase the risk of damage to structures.

Epicenter

Deposits of soft clay occur throughout New York State.  These deposits were left when vast glacial lakes covered the state during the Ice Age.  The larger glacial lakes include the various levels of Glacial Lake Albany (filling in the Hudson River and Champlain valleys), Glacial Lake Iroquois (larger form of Lake Ontario), Champlain Sea (filling portions of Lake Champlain and St. Lawrence River), and numerous smaller valley fill lakes throughout the state. In such areas, the 5.8 magnitude central Virginia earthquake on August 23, 2011 was strongly felt. In other, even adjacent areas on bedrock, the earthquake was not felt at all.


 

Read more about Earthquakes and their history in New York State »

 


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