Reviewed by USGSGuam55y ago
M6.5 earthquake 276 km SW of Merizo Village, Guam
Saturday, October 23, 1971, 22:33:32 UTC · 11.886°N, 142.552°E
A magnitude 6.5 earthquake struck 276 km SW of Merizo Village, Guam on Saturday, October 23, 1971, 22:33:32 UTC, at a depth of 22.9 km (shallow). It is the strongest earthquake within 300 km since an M6.7 on October 18, 1935.
- Magnitude
- 6.5
- Strong · mw
- Depth
- 23 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
97 kilotons of TNT
That is about 6 times the Hiroshima bomb. It released about 204 times the energy of a magnitude 5.0.
Tectonic setting
58 km
from the nearest mapped plate boundary, between the Philippine Sea and Mariana plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
23 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 4 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M6.5 on October 24, 1971. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
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:
- 7.2265 km S of Merizo Village, GuamJanuary 28, 1931 · 237 km SE of this epicenter
- 7.1261 km S of Merizo Village, GuamMay 9, 1917 · 229 km SE of this epicenter
- 7.098 km SSE of Inarajan Village, GuamDecember 9, 1909 · 267 km E of this epicenter
- 6.7Mariana Islands regionOctober 18, 1935 · 141 km NW of this epicenter
- 6.596 km ENE of Fais, MicronesiaMarch 15, 1943 · 248 km SW of this epicenter
- 6.4279 km S of Merizo Village, GuamMay 6, 1917 · 218 km SE of this epicenter
- 6.3193 km ENE of Fais, MicronesiaMarch 30, 1919 · 157 km S of this epicenter
- 6.3146 km WSW of Merizo Village, GuamNovember 24, 1917 · 136 km NE of this epicenter
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 · 249 km away · intensity IX
Severe damage ($5–24M)tsunami
- 1909M8.0
Guam
9 Dec 1909 · 275 km away · intensity VIII
Moderate damage ($1–5M)tsunami
- 1892M7.5
Guam
16 May 1892 · 249 km away · intensity VIII
Moderate damage ($1–5M)tsunami
- 1825
Ladrones Island
Apr 1825 · 249 km away · intensity VIII
Moderate damage ($1–5M)tsunami
- 1834
Agana
May 1834 · 249 km away
Moderate damage ($1–5M)
- 1903
Guam
10 Feb 1903 · 249 km away · intensity VII
Limited damage (under $1M)tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.