Reviewed by USGSIndia region54y ago
M6.6 earthquake in Nicobar Islands, India region
Saturday, April 7, 1973, 03:00:58 UTC · 6.966°N, 91.384°E
A magnitude 6.6 earthquake struck in Nicobar Islands, India region on Saturday, April 7, 1973, 03:00:58 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M7.0 on May 17, 1955.
- Magnitude
- 6.6
- Strong · ms
- Depth
- 33 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: 100 km aftershock search area
In context
How big was it, and why here?
Energy released
120 kilotons of TNT
That is about 8 times the Hiroshima bomb. It released about 251 times the energy of a magnitude 5.0.
Tectonic setting
86 km
from the nearest mapped plate boundary, between the Indian and Burma plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
33 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 100 km
USGS lists 1 M2.5+ earthquake within 100 km in the following 30 days; the largest was M4.8 on April 7, 1973. 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 22 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.0190 km WNW of Sabang, IndonesiaMay 17, 1955 · 275 km E of this epicenter
- 6.8238 km WNW of Sabang, IndonesiaJanuary 20, 1917 · 232 km E of this epicenter
- 6.6249 km NW of Sabang, IndonesiaMarch 5, 1921 · 253 km E of this epicenter
- 6.5253 km WNW of Sabang, IndonesiaNovember 21, 1907 · 197 km E of this epicenter
- 6.3184 km W of Banda Aceh, IndonesiaNovember 25, 1935 · 293 km SE of this epicenter
- 6.3off the west coast of northern SumatraNovember 30, 1937 · 215 km S of this epicenter
- 6.3Nicobar Islands, India regionSeptember 15, 1964 · 281 km NE of this epicenter
- 6.2Nicobar Islands, India regionAugust 12, 1915 · 58 km N of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 3 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1881M7.9
Andaman I,Nicobar I
31 Dec 1881 · 208 km away
Severe damage ($5–24M)tsunami
- 1847
Little Nicobar Island
31 Oct 1847 · 255 km away · intensity X
Limited damage (under $1M)tsunami
- 1955M7.3
Little Nicobar Island
17 May 1955 · 293 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.