M6.4 earthquake in Southwest Indian Ridge

Monday, March 21, 1927, 15:05:37 UTC · 33.605°S, 57.685°E

A magnitude 6.4 earthquake struck in Southwest Indian Ridge on Monday, March 21, 1927, 15:05:37 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M7.0 on September 2, 1926.

Magnitude: 6.4; Strong · mw
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: 100 km aftershock search area

In context

How big was it, and why here?

Energy released

60 kilotons of TNT

That is about 4 times the Hiroshima bomb. It released about 126 times the energy of a magnitude 5.0.

Tectonic setting

58 km

from the nearest mapped plate boundary, between the Somali 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 100 km

USGS lists 1 M2.5+ earthquake within 100 km in the following 30 days; the largest was M6.3 on April 16, 1927. 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.

6.3South Indian Ocean100y ago · 97 km SE of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 13 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

Nearby trackers