Reviewed by USGSCosta Rica88y ago
M7.6 earthquake 4 km WNW of Atenas, Costa Rica
Thursday, December 21, 1939, 20:54:52 UTC · 9.990°N, 84.412°W
A magnitude 7.6 earthquake struck 4 km WNW of Atenas, Costa Rica on Thursday, December 21, 1939, 20:54:52 UTC, at a depth of 25.0 km (shallow). No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.
- Magnitude
- 7.6
- Major · mw
- Depth
- 25 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 200 km aftershock search area
In context
How big was it, and why here?
Energy released
3.7 megatons of TNT
That is about 243 times the Hiroshima bomb. It released about 7,674 times the energy of a magnitude 5.0.
Tectonic setting
59 km
from the nearest mapped plate boundary, between the Panama and Caribbean plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
25 km
Shallow earthquakes (under 70 km) produce the strongest surface shaking for their size, so they are the ones most likely to cause damage near the epicenter.
Did You Feel It?
Where it was felt
No “Did You Feel It?” reports have been published for this event yet. If you felt it, you can add your report on the USGS website.
I felt it — report to USGS ↗USGS PAGER estimate
Who was exposed to shaking
USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No PAGER estimate is available for this event.
After the main event
Aftershocks within 200 km
USGS lists 2 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.8 on December 22, 1939. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 38 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.392 km SW of San Juan del Sur, NicaraguaDecember 30, 1907 · 240 km W of this epicenter
- 7.353 km SSE of Quepos, Costa RicaDecember 20, 1904 · 121 km S of this epicenter
- 7.16 km WNW of Siquirres, Costa RicaApril 24, 1916 · 94 km E of this epicenter
- 6.847 km S of Masachapa, NicaraguaOctober 2, 1932 · 282 km NW of this epicenter
- 6.820 km SSE of Guarumal, PanamaJuly 21, 1934 · 293 km SE of this epicenter
- 6.718 km WSW of Nicoya, Costa RicaJanuary 20, 1905 · 131 km W of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 25 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 700 recorded deaths. The most severe:
- 1910M6.4
Cartago, San Jose
4 May 1910 · 45 km away
700 deathsSevere damage ($5–24M)
- 1854M7.3
Costa Rica-Panama
5 Aug 1854 · 227 km away
Severe damage ($5–24M)tsunami
- 1925M6.7
Managua
5 Oct 1925 · 260 km away
Severe damage ($5–24M)
- 1922M6.4
Nicaragua
16 Feb 1922 · 234 km away
Severe damage ($5–24M)
- 1888
San Jose, Ala Juela, Heredia
30 Dec 1888 · 34 km away · intensity VIII
Severe damage ($5–24M)
- 1898M7.9
Leon, Chinandega, Managua
29 Apr 1898 · 283 km away · intensity VIII
Moderate damage ($1–5M)
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.