QuakeScout
Magnitude5.3

Reviewed by USGSTonga49y ago

M5.3 earthquake 224 km SSW of ‘Ohonua, Tonga

Monday, August 15, 1977, 05:41:12 UTC · 23.325°S, 175.382°W

A magnitude 5.3 earthquake struck 224 km SSW of ‘Ohonua, Tonga on Monday, August 15, 1977, 05:41:12 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.5 on July 9, 1977.

Magnitude
5.3
Moderate · mb
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: 75 km aftershock search area

In context

How big was it, and why here?

Energy released

1 kilotons of TNT

That is about 1/11 of the Hiroshima bomb. It released about 3 times the energy of a magnitude 5.0.

Tectonic setting

53 km

from the nearest mapped plate boundary, between the Kermadec and Tonga 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 75 km

USGS lists 1 M2.5+ earthquake within 75 km in the following 30 days; the largest was M4.3 on September 13, 1977. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

M3M4M51h6h1d3d7d14d30dMainshock M5.3
Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.
  1. 4.3169 km SSW of ‘Ohonua, Tonga49y ago · 56 km N of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 235 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

  1. 7.8south of TongaOctober 11, 1975 · 176 km S of this epicenter
  2. 7.6south of the Fiji IslandsDecember 18, 1963 · 217 km SW of this epicenter
  3. 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 280 km NE of this epicenter
  4. 7.4south of TongaMarch 18, 1905 · 232 km SE of this epicenter
  5. 7.2south of the Fiji IslandsNovember 24, 1960 · 174 km SW of this epicenter
  6. 6.8Tonga regionJune 22, 1977 · 73 km NW of this epicenter
  7. 6.7south of the Fiji IslandsSeptember 8, 1920 · 157 km SW of this epicenter
  8. 6.7south of the Fiji IslandsAugust 12, 1967 · 251 km SW 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:

  1. 1977M7.2

    Tonga Trench

    22 Jun 1977 · 73 km away · intensity IV

    1 death$1 million damagetsunami

  2. 1937M8.1

    Fiji Islands

    16 Apr 1937 · 262 km away

  3. 1948M7.9

    Tonga Islands

    8 Sep 1948 · 295 km away

    tsunami

  4. 1975M7.8

    S Of Tonga

    11 Oct 1975 · 176 km away

  5. 1963M7.5

    Tonga Trench

    18 Dec 1963 · 205 km away

    tsunami

  6. 1977M7.2

    Tonga Trench

    10 Oct 1977 · 281 km away

    tsunami

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

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