M7.2 earthquake 19 km ENE of Hihifo, Tonga

Monday, October 15, 1984, 10:21:07 UTC · 15.860°S, 173.643°W

A magnitude 7.2 earthquake struck 19 km ENE of Hihifo, Tonga on Monday, October 15, 1984, 10:21:07 UTC, at a depth of 128.4 km (intermediate). It is the strongest earthquake within 300 km since an M7.7 on September 1, 1981.

Magnitude: 7.2; Major · mw
Depth: 128 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 earthquakeDashed circle: 200 km aftershock search area

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

90 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

128 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 lists 7 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.6 on October 30, 1984. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 611 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 5 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 2 recorded deaths. The most severe:

1917M8.3
Samoa Islands
26 Jun 1917 · 80 km away
2 deathsModerate damage ($1–5M)tsunami
1981M7.7
Apia; American Samoa: Pago Pago
1 Sep 1981 · 117 km away · intensity VI
Limited damage (under $1M)tsunami
1977M7.6
Apia
2 Apr 1977 · 190 km away · intensity VI
Limited damage (under $1M)tsunami
1975M7.8
Samoa Islands
26 Dec 1975 · 133 km away · intensity V
tsunami
1957M7.5
Samoa Islands
14 Apr 1957 · 80 km away

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

Nearby trackers