Saturday, October 27, 2007

New England Earthquakes and Their Aftershocks

Earthquake Shakes Bay State - Boston News Story - WCVB Boston: "BOSTON -- For the second time this month, an earthquake has hit Massachusetts."

This earthquake happened while I was visiting Anna in New Haven. It was an interesting little story, but what struck me was this last sentence:
Earlier this month, a quake measuring 1.8 on the Richter scale rattled homes in Amesbury and Merrimac. Officials said that the quake was a late aftershock of an earthquake from 1727 in Newburyport.
Can aftershocks linger for 280 years? I went to the United States Geological Survey site to learn more. First, about the Newburyport earthquake:
At Newbury, many stone walls and chimney bricks were shaken down, and almost all tops of chimneys were knocked off. Considerable changes occurred in the flow of water in springs and, in some springs, changes occurred in the character of the water. "Some firm land became quagmire, and marshes were dried up." The rise and fall of the ground made it difficult to walk, and houses shook and rocked as if they would fall apart. Sand blows were reported near Spring Island. Felt from the Kennebec River in Maine to the Delaware River on the New York-Pennsylvania border and from ships at sea to the "extreme western settlements." Aftershocks occurred in the area for several months. The strongest aftershock (MM intensity V) occurred in the Newbury area on Dec. 28, 1727, and Jan. 4 and Feb. 10, 1728 (local dates).
Second, the definition of aftershock:
"Foreshock" and "aftershock" are relative terms. Foreshocks are earthquakes which precede larger earthquakes in the same location. Aftershocks are smaller earthquakes which occur in the same general area during the days to years following a larger event or "mainshock", defined as within 1-2 fault lengths away and during the period of time before the background seismicity level has resumed. As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the main shock. The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30km) are much less likely to be followed by aftershocks than shallow earthquakes. (Univ. of Washington)
So yes, it is possible, I suppose, for the 1.8 quake earlier this month to be an aftershock from 1727. I don't know if it is, though. I could not find any other source to confirm it.



  1. nice pic, perfect for the theme. happy sunday!

  2. You're kidding...I used to live in LA area, earthquake centeral, and now I live in earthquake subburbia.

  3. I'm with you, Andree. How can they tell it's an aftershock from the earthquake 280 years ago? If that's the case, all earthquakes are aftershocks from each other, right? You know, a bit like the domino effect...

  4. i remember running down a 10 storey building in panic n screams everywhere...but the building didnt topplebut it did sway. Malaysia doesnt experience destructive earthquakes but we feel it

  5. I was chuckling at the idea of this small quake being an aftershock of one in 1727. I think you did a good job of researching the question but I really am skeptical about that being the case. And I have a hard time considering a 1.8 a true quake, after having experienced a 5.6 one here around 15 years ago. That one made my little house rock and roll! ;-)

  6. Very interesting post! I have always thought that an aftershock had to occur within a few hours or days of the main event. How fascinating that it could occur hundreds of years later!


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