Reviewed by USGSTonga49y ago
M4.9 earthquake 137 km WSW of Haveluloto, Tonga
Saturday, July 23, 1977, 09:14:19 UTC · 21.643°S, 176.427°W
A magnitude 4.9 earthquake struck 137 km WSW of Haveluloto, Tonga on Saturday, July 23, 1977, 09:14:19 UTC, at a depth of 294.0 km (intermediate). It is the strongest earthquake within 300 km since an M5.1 on July 19, 1977.
- Magnitude
- 4.9
- Light · mb
- Depth
- 294 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
338 tons of TNT
That is about 1/45 of the Hiroshima bomb. A magnitude 5.0 releases about 1 times more energy.
Tectonic setting
4 km
from the nearest mapped plate boundary, between the Tonga and Australian plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: intermediate
294 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 50 km
USGS has not published any M2.5+ earthquake within 50 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 354 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.0TongaJanuary 4, 1903 · 235 km NE of this epicenter
- 7.8159 km W of Pangai, TongaDecember 14, 1950 · 223 km N of this epicenter
- 7.8111 km SSE of Pangai, TongaJune 26, 1913 · 292 km E of this epicenter
- 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 267 km E of this epicenter
- 7.5262 km WNW of Haveluloto, TongaMay 21, 1962 · 203 km NW of this epicenter
- 7.4Fiji regionSeptember 28, 1957 · 234 km NW of this epicenter
- 7.3227 km WNW of Haveluloto, TongaApril 16, 1937 · 148 km NW of this epicenter
- 7.2Fiji regionOctober 9, 1967 · 290 km W of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 9 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 1 recorded deaths. The most severe:
- 1977M7.2
Tonga Trench
22 Jun 1977 · 148 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 61 km away
- 1903M8.0
Tonga Islands
4 Jan 1903 · 235 km away
- 1948M7.9
Tonga Islands
8 Sep 1948 · 261 km away
tsunami
- 1950M7.7
Tonga Islands
14 Dec 1950 · 242 km away · intensity VI
- 1957M7.5
Fiji Islands
28 Sep 1957 · 256 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.