M5.6 earthquake in Pacific-Antarctic Ridge

Saturday, July 31, 2004, 01:51:31 UTC · 63.204°S, 165.665°W

A magnitude 5.6 earthquake struck in Pacific-Antarctic Ridge on Saturday, July 31, 2004, 01:51:31 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M5.9 on November 21, 1999.

Magnitude: 5.6; 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

4 kilotons of TNT

That is about 1/4 of the Hiroshima bomb. It released about 8 times the energy of a magnitude 5.0.

Tectonic setting

33 km

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

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 8 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M6.0 on August 1, 2004. 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 20 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

Nearby trackers