The December 20, 1940 earthquake
M5.3near Tamworth, New Hampshire
A magnitude 5.3 earthquake 6.2 miles deep, centred in Carroll County. The 2nd strongest in New Hampshire’s record since 1900, and the strongest within 50 miles in the catalogue, which runs from 1900. 1 aftershock of magnitude 2.5 or more followed within 30 days.
The earthquake
- Magnitude
- 5.3
- moment magnitude (mw)
- Depth
- 6.2 mi
- 10.0 km below the surface
- Local time
- Friday, December 20, 1940
- 02:27 EST; 07:27 UTC
- In New Hampshire’s record
- 2nd
- strongest of 44 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event ushis1343 (“8 km W of Tamworth, New Hampshire”). The USGS event page carries the ShakeMap, felt reports and the official summary.
Aftershocks
Earthquakes of magnitude 2.5 or more within 20 miles of the epicentre in the 30 days after.
1
Aftershocks in 30 days
5.6
Largest aftershock, Dec 24, 1940 · its page
0
On the first day
0
In the 7 days before
- The search radius is the surface rupture length expected for an earthquake of this magnitude (Wells and Coppersmith, 1994), at least 20 and at most 600 miles, so a great earthquake's sequence is counted along its whole fault.
- Before the modern seismic networks of the 1970s many small aftershocks went unrecorded, so early sequences read short.
Counties and cities within 50 miles
Distance from the epicentre to each county boundary (zero when inside) and to each city centre.
Counties
- Carroll CountyNH · inside
- Grafton CountyNH · 3.1 mi
- Belknap CountyNH · 11.1 mi
- Coos CountyNH · 14.9 mi
- York CountyME · 19.8 mi
- Oxford CountyME · 19.8 mi
- Strafford CountyNH · 24.0 mi
- Merrimack CountyNH · 27.7 mi
- Cumberland CountyME · 28.3 mi
- Orange CountyVT · 35.9 mi
- Sullivan CountyNH · 36.9 mi
- Caledonia CountyVT · 38.8 mi
- Essex CountyVT · 40.0 mi
- Rockingham CountyNH · 41.7 mi
- Windsor CountyVT · 42.2 mi
- Androscoggin CountyME · 45.6 mi
Earthquakes around the epicentre
14 earthquakes of magnitude 3 or more within 50 miles of this epicentre since 1973.
No earlier earthquake of magnitude 5 or more within 50 miles in the catalogue since 1900.
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.