M4.9 earthquake off the west coast of the South Island of New Zealand

Monday, August 17, 2009, 16:56:42 UTC · 45.830°S, 166.039°E

A magnitude 4.9 earthquake struck off the west coast of the South Island of New Zealand on Monday, August 17, 2009, 16:56:42 UTC, at a depth of 35.0 km (shallow). It is the strongest earthquake within 300 km since an M4.9 on August 7, 2009.

Magnitude: 4.9; Light · mwc
Depth: 35 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: 50 km aftershock search area

In context

How big was it, and why here?

Energy released

338 tons of TNT

That is about 1/45 of the Hiroshima bomb. A magnitude 5.0 releases about 1 times more energy.

Tectonic setting

2 km

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

Depth: shallow

35 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 50 km

USGS lists 7 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.2 on August 25, 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 99 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 6 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

2009M7.8
Off West Coast Of South Island
15 Jul 2009 · 41 km away
Limited damage (under $1M)tsunami
2003M7.2
Dunedin,Invercargill,Te Anau,Fiordland
21 Aug 2003 · 118 km away
Limited damage (under $1M)tsunami
2004M7.1
Invercargill, Southland, Otago
22 Nov 2004 · 138 km away
Limited damage (under $1M)tsunami
2007M6.8
South Island: Fiordland
15 Oct 2007 · 168 km away
Limited damage (under $1M)
1826M8.0
Fjordland
1826 · 36 km away
1979M7.5
W Of North Island
12 Oct 1979 · 97 km away · intensity V

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

Nearby trackers