M5.5 earthquake 47 km ENE of Hihifo, Tonga

Wednesday, October 28, 2009, 23:56:40 UTC · 15.794°S, 173.388°W

A magnitude 5.5 earthquake struck 47 km ENE of Hihifo, Tonga on Wednesday, October 28, 2009, 23:56:40 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M6.0 on October 19, 2009.

Magnitude: 5.5; Moderate · mwc
Depth: 10 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

3 kilotons of TNT

That is about 1/6 of the Hiroshima bomb. It released about 6 times the energy of a magnitude 5.0.

Tectonic setting

107 km

from the nearest mapped plate boundary, between the Tonga and Pacific plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.

Depth: shallow

10 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 10 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M5.8 on November 1, 2009. 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 1,470 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 10 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 194 recorded deaths. The most severe:

2009M8.1
Samoa Islands
29 Sep 2009 · 143 km away
192 deaths$285 million damagetsunami
1917M8.3
Samoa Islands
26 Jun 1917 · 53 km away
2 deathsModerate damage ($1–5M)tsunami
1919M8.1
Tonga Islands
30 Apr 1919 · 299 km away
Limited damage (under $1M)tsunami
1981M7.7
Apia; American Samoa: Pago Pago
1 Sep 1981 · 98 km away · intensity VI
Limited damage (under $1M)tsunami
1977M7.6
Apia
2 Apr 1977 · 171 km away · intensity VI
Limited damage (under $1M)tsunami
1975M7.8
Samoa Islands
26 Dec 1975 · 111 km away · intensity V
tsunami

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

Nearby trackers