M6.8 earthquake 150 km N of Opotiki, New Zealand

Sunday, December 30, 1984, 21:36:56 UTC · 36.663°S, 177.512°E

A magnitude 6.8 earthquake struck 150 km N of Opotiki, New Zealand on Sunday, December 30, 1984, 21:36:56 UTC, at a depth of 39.3 km (shallow). It is the strongest earthquake within 300 km since an M7.6 on May 17, 1947.

Magnitude: 6.8; Strong · mw
Depth: 39 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: 100 km aftershock search area

In context

How big was it, and why here?

Energy released

239 kilotons of TNT

That is about 16 times the Hiroshima bomb. It released about 501 times the energy of a magnitude 5.0.

Tectonic setting

11 km

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

Depth: shallow

39 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 100 km

USGS lists 24 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M5.7 on January 8, 1985. 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 104 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 11 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 1 recorded deaths. The most severe:

1914
North Island
6 Oct 1914 · 140 km away · intensity VIII
1 deathModerate damage ($1–5M)tsunami
1932M6.8
Gisborne, Wairoa
15 Sep 1932 · 260 km away
Moderate damage ($1–5M)tsunami
1947M7.1
Off Coast North Island
25 Mar 1947 · 271 km away · intensity IV
Limited damage (under $1M)tsunami
1956M5.3
North Island
2 Mar 1956 · 295 km away · intensity VII
Limited damage (under $1M)tsunami
1880M7.0
Gisborne
8 Sep 1880 · 270 km away
tsunami
1947M6.9
Off Coast North Island
17 May 1947 · 230 km away
tsunami

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

Nearby trackers