M6.5 earthquake 293 km WSW of Merizo Village, Guam

Sunday, October 24, 1971, 01:37:29 UTC · 11.880°N, 142.363°E

A magnitude 6.5 earthquake struck 293 km WSW of Merizo Village, Guam on Sunday, October 24, 1971, 01:37:29 UTC, at a depth of 15.0 km (shallow). It is the strongest earthquake within 300 km since an M6.5 on October 23, 1971.

Magnitude: 6.5; Strong · mw
Depth: 15 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

88 kilotons of TNT

That is about 6 times the Hiroshima bomb. It released about 184 times the energy of a magnitude 5.0.

Tectonic setting

61 km

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

Depth: shallow

15 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 3 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M6.2 on October 24, 1971. 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 57 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 7 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1849M7.5
Guam
25 Jan 1849 · 257 km away · intensity IX
Severe damage ($5–24M)tsunami
1909M8.0
Guam
9 Dec 1909 · 295 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1892M7.5
Guam
16 May 1892 · 257 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1825
Ladrones Island
Apr 1825 · 257 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1834
Agana
May 1834 · 257 km away
Moderate damage ($1–5M)
1903
Guam
10 Feb 1903 · 257 km away · intensity VII
Limited damage (under $1M)tsunami

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

Nearby trackers