1940 New Hampshire earthquakes

The 1940 New Hampshire earthquakes struck on December 20 and again on December 24. Both shocks had an estimated Ms magnitude of 5.6, and a maximum Mercalli intensity of VII (Very strong). These doublet earthquakes were the largest to hit the state in several hundred years. Damage included minor fractures or knocked over chimneys in a zone extending through New Hampshire and four other states: Maine, New York, Vermont and Massachusetts.[5]

1940 New Hampshire earthquakes
UTC timeDoublet earthquake:    
 A: 1940-12-20 07:27:26
 B: 1940-12-24 13:43:44
ISC event 
 A: 901740
 B: 901745
USGS-ANSSn/a
Local date20 December 1940 (1940-12-20)
Local time
Magnitude 
 A: 5.5 mN[1]     5.6 MGR(PAS) ,[2]     5.25 Mw  (est.)[3]
 B: 5.5 mN[1]     5.6 MGR(PAS) [4]     5.50 Mw  (est.)[3]
Depth35 km (22 mi)[2]
Epicenter43.83°N 71.28°W / 43.83; -71.28 [1]
TypeUnknown
Areas affectedNew England
United States
Max. intensityVII (Very strong) [1]
Isoseismal map for the 1940 New Hampshire earthquakes

History

While not known for earthquakes, New Hampshire has been dotted with both major and minor events. Two examples of strong earthquakes occurred in the 17th century. One was the 1638 earthquake; the other significant event to strike the state was the 1663 Charlevoix earthquake, originating in the Saint Lawrence River fault zone. The extent of the earthquake is not firm, at least in the state, as the population was composed largely of colonial settlers who had left the east coast. The 1663 earthquake felled chimneys, oscillated houses, and threw pewter from shelves in the Massachusetts Bay area.[6]

Geography

Reports of the 1940 earthquake extended as far north as Montreal and Quebec in Canada, and included Maine, New York, New Jersey, Pennsylvania, northeastern Delaware, Massachusetts, Vermont and Rhode Island.[7] The epicenter was next to the Ossipee Mountains, near the town of Ossipee, New Hampshire. These mountains are the remains of an ancient volcanic ring dike.[8] A similar ring dike can be seen in southern New Hampshire at Pawtuckaway State Park.

Damage

Both earthquakes had surface magnitudes estimated at 5.5 and a Mercalli intensity of VII,[9] and spawned waves of minor damage. There were reports of fractured pipes, walls, and furniture, as well as "fallen plaster" near the epicenter.[7] The number of chimneys damaged totaled 20, in addition to fallen ones. The earthquake caused damage to wells, turning the water brown[7] and displayed strength by movement, causing five monuments to shift from their original position at a cemetery, and moving one old house in the village of Wonalancet roughly 12 inches (30 cm). The earthquake additionally shifted objects as heavy as stoves. Aftershocks of the earthquake occurred over the next several months.[7]

See also

Notes
  1. Stover & Coffman 1993.
  2. ISC-OB Event 901740 [IRIS].
  3. Stover & Coffman 1993, p. 308.
  4. ISC-OB Event 901745 [IRIS].
  5. Stover & Coffman 1993, p. 308.
  6. "New Hampshire – Earthquake History". United States Geological Survey. October 21, 2009. Archived from the original on December 15, 2009. Retrieved December 24, 2009.
  7. "Historic Earthquakes". United States Geological Survey. October 21, 2009. Retrieved December 20, 2009.
  8. Hall, Anthony, Igneous Petrology, Longman, 1987 p.75–76 ISBN 0-582-30174-2
  9. Stover & Coffman 1993, p. 308. The surface magnitudes are from Gutenberg & Richter (1954).

Sources
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