QuakeScout
Magnitude4.6

Reviewed by USGSTonga42y ago

M4.6 earthquake 86 km SW of Hihifo, Tonga

Wednesday, October 31, 1984, 21:36:40 UTC · 16.597°S, 174.264°W

A magnitude 4.6 earthquake struck 86 km SW of Hihifo, Tonga on Wednesday, October 31, 1984, 21:36:40 UTC, at a depth of 191.5 km (intermediate). It is the strongest earthquake within 300 km since an M4.6 on October 30, 1984.

Magnitude
4.6
Light · mb
Depth
192 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

120 tons of TNT

That is about 1/126 of the Hiroshima bomb. A magnitude 5.0 releases about 4 times more energy.

Tectonic setting

30 km

from the nearest mapped plate boundary, between the Tonga and Niuafo'ou plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.

Depth: intermediate

192 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 699 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

  1. 8.11919 Tonga EarthquakeApril 30, 1919 · 272 km SE of this epicenter
  2. 8.0The 1917 Samoa-Tonga EarthquakeJune 26, 1917 · 207 km NE of this epicenter
  3. 7.8146 km ESE of Hihifo, TongaDecember 26, 1975 · 195 km E of this epicenter
  4. 7.7133 km NE of Hihifo, TongaSeptember 1, 1981 · 221 km NE of this epicenter
  5. 7.6199 km ESE of Hihifo, TongaApril 2, 1977 · 231 km E of this epicenter
  6. 7.4103 km ESE of Neiafu, TongaFebruary 27, 1921 · 288 km SE of this epicenter
  7. 7.385 km ESE of Neiafu, TongaJanuary 2, 1907 · 293 km S of this epicenter
  8. 7.219 km ENE of Hihifo, TongaOctober 15, 1984 · 105 km NE of this epicenter

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 7 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 2 recorded deaths. The most severe:

  1. 1917M8.3

    Samoa Islands

    26 Jun 1917 · 182 km away

    2 deathsModerate damage ($1–5M)tsunami

  2. 1919M8.1

    Tonga Islands

    30 Apr 1919 · 269 km away

    Limited damage (under $1M)tsunami

  3. 1981M7.7

    Apia; American Samoa: Pago Pago

    1 Sep 1981 · 221 km away · intensity VI

    Limited damage (under $1M)tsunami

  4. 1977M7.6

    Apia

    2 Apr 1977 · 231 km away · intensity VI

    Limited damage (under $1M)tsunami

  5. 1975M7.8

    Samoa Islands

    26 Dec 1975 · 195 km away · intensity V

    tsunami

  6. 1957M7.5

    Samoa Islands

    14 Apr 1957 · 182 km away

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

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