Reviewed by USGSTonga116y ago
M7.2 earthquake 241 km WNW of Houma, Tonga
Monday, August 21, 1911, 16:28:54 UTC · 20.004°S, 177.265°W
A magnitude 7.2 earthquake struck 241 km WNW of Houma, Tonga on Monday, August 21, 1911, 16:28:54 UTC, at a depth of 230.0 km (intermediate). It is the strongest earthquake within 300 km since an M7.2 on December 14, 1910.
- Magnitude
- 7.2
- Major · mB
- Depth
- 230 km
- Intermediate
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquake
In context
How big was it, and why here?
Energy released
951 kilotons of TNT
That is about 63 times the Hiroshima bomb. It released about 1,995 times the energy of a magnitude 5.0.
Tectonic setting
114 km
from the nearest mapped plate boundary, between the Tonga and Australian plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.
Depth: intermediate
230 km
Intermediate-depth earthquakes usually break inside a plate that is sinking into the mantle. Shaking spreads over a wide area but is gentler at the epicenter than a shallow quake of the same size.
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 has not published any M2.5+ earthquake within 200 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 8 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.0TongaJanuary 4, 1903 · 237 km E of this epicenter
- 7.6178 km E of Levuka, FijiFebruary 22, 1909 · 272 km NW of this epicenter
- 7.4227 km E of Levuka, FijiAugust 21, 1910 · 278 km NW of this epicenter
- 7.2Fiji regionMarch 31, 1907 · 216 km N of this epicenter
- 7.2280 km WNW of Houma, TongaDecember 14, 1910 · 72 km SW of this epicenter
- 7.0254 km WNW of Houma, TongaApril 20, 1910 · 40 km SW of this epicenter
- 6.915 km WSW of Pangai, TongaFebruary 27, 1905 · 290 km E of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 4 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1903M8.0
Tonga Islands
4 Jan 1903 · 237 km away
- 1909M7.8
Fiji Islands
22 Feb 1909 · 288 km away
- 1853
Tonga Trench
24 Dec 1853 · 254 km away
tsunami
- 1907
S Of Tonga
1907 · 206 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.