Reviewed by USGS43y ago
M4.7 earthquake in Chagos Archipelago region
Tuesday, December 20, 1983, 12:12:42 UTC · 6.663°S, 72.215°E
A magnitude 4.7 earthquake struck in Chagos Archipelago region on Tuesday, December 20, 1983, 12:12:42 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M5.5 on December 17, 1983.
- Magnitude
- 4.7
- Light · mb
- Depth
- 10 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: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
169 tons of TNT
That is about 1/89 of the Hiroshima bomb. A magnitude 5.0 releases about 3 times more energy.
Tectonic setting
17 km
from the nearest mapped plate boundary, between the Indian and Australian plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
10 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 50 km
USGS lists 4 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.1 on December 20, 1983. 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 36 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.3Chagos Archipelago regionNovember 30, 1983 · 24 km SW of this epicenter
- 6.3Chagos Archipelago regionDecember 3, 1983 · 91 km W of this epicenter
- 6.3Chagos Archipelago regionSeptember 12, 1965 · 165 km W of this epicenter
- 6.2Chagos Archipelago regionMay 11, 1912 · 161 km W of this epicenter
- 6.0Chagos Archipelago regionOctober 2, 1957 · 282 km W of this epicenter
- 5.9Chagos Archipelago regionNovember 11, 1967 · 112 km NW of this epicenter
- 5.9Chagos Archipelago regionMarch 2, 1968 · 106 km NW of this epicenter
- 5.7Chagos Archipelago regionNovember 11, 1967 · 123 km NW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 1 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1983M7.6
Chagos Archipelago: Diego Garcia
30 Nov 1983 · 24 km away · intensity VI
Limited damage (under $1M)tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.