M7.6 earthquake in Kermadec Islands region

Wednesday, July 6, 2011, 19:03:18 UTC · 29.539°S, 176.340°W

A magnitude 7.6 earthquake struck in Kermadec Islands region on Wednesday, July 6, 2011, 19:03:18 UTC, at a depth of 17.0 km (shallow). USGS received 17 “Did You Feel It?” reports, with a maximum reported intensity of III (weak). It is the strongest earthquake within 300 km since an M7.7 on October 20, 1986.

Magnitude: 7.6; Major · mww
Depth: 17 km; Shallow
Felt reports: 17; Max intensity III
Est. shaking: VII; Very strong (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

3.8 megatons of TNT

That is about 252 times the Hiroshima bomb. It released about 7,943 times the energy of a magnitude 5.0.

Tectonic setting

14 km

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

Depth: shallow

17 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

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

Place	Intensity	Reports	Distance
Wellington, Wellington, New Zealand	II · Weak	4	1532 km
Suva, Central, Fiji Islands	III · Weak	2	1371 km
Gisborne, Gisborne, New Zealand	II · Weak	2	1137 km
Manukau, Auckland, New Zealand	II · Weak	1	1163 km
Hastings, Hawkeʿs Bay, New Zealand	II · Weak	1	1283 km
Nukuʿalofa, Tongatapu, Tonga	II · Weak	1	937 km
Gold Coast, Queensland, Australia	II · Weak	1	2954 km
Auckland, Auckland, New Zealand	II · Weak	1	1160 km
Christchurch, Canterbury, New Zealand	II · Weak	1	1839 km

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 222 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.0 on July 9, 2011. 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 1,572 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 14 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1986M8.1
Raoul
20 Oct 1986 · 158 km away
Limited damage (under $1M)tsunami
1976M7.9
Kermadec Islands
14 Jan 1976 · 114 km away
Limited damage (under $1M)tsunami
1968M7.3
S Of, Raoul
25 Jul 1968 · 243 km away
Limited damage (under $1M)tsunami
1917M8.0
Kermadec Islands
1 May 1917 · 74 km away
tsunami
1955M7.8
Kermadec Islands
27 Feb 1955 · 190 km away
1976M7.8
Kermadec Islands
14 Jan 1976 · 95 km away · intensity VIII

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

Nearby trackers