Reviewed by USGS86y ago
M7.7 earthquake in Mariana Islands region
Saturday, December 28, 1940, 16:37:44 UTC · 18.204°N, 147.462°E
A magnitude 7.7 earthquake struck in Mariana Islands region on Saturday, December 28, 1940, 16:37:44 UTC, at a depth of 15.0 km (shallow). No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.
- Magnitude
- 7.7
- Major · 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 earthquake
In context
How big was it, and why here?
Energy released
5.4 megatons of TNT
That is about 355 times the Hiroshima bomb. It released about 11,220 times the energy of a magnitude 5.0.
Tectonic setting
37 km
from the nearest mapped plate boundary, between the Mariana 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 200 km
USGS has not published any M2.5+ earthquake within 200 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 11 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.5Mariana Islands regionJanuary 17, 1940 · 134 km SE of this epicenter
- 7.2Pagan region, Northern Mariana IslandsOctober 24, 1930 · 86 km W of this epicenter
- 6.6Alamagan region, Northern Mariana IslandsFebruary 10, 1921 · 98 km SW of this epicenter
- 6.5258 km NE of Saipan, Northern Mariana IslandsDecember 1, 1938 · 130 km S of this epicenter
- 6.5Pagan region, Northern Mariana IslandsOctober 28, 1930 · 95 km W of this epicenter
- 6.3215 km ENE of Saipan, Northern Mariana IslandsMarch 19, 1932 · 236 km S of this epicenter
- 6.0Pagan region, Northern Mariana IslandsDecember 25, 1934 · 85 km NW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 1 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1902M8.1
Agana
22 Sep 1902 · 156 km away · intensity IX
Severe damage ($5–24M)
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.