Reviewed by USGSAlaska1y ago
M3.9 earthquake 73 km ESE of Sand Point, Alaska
Wednesday, October 16, 2024, 20:48:58 UTC · 55.115°N, 159.406°W
A magnitude 3.9 earthquake struck 73 km ESE of Sand Point, Alaska on Wednesday, October 16, 2024, 20:48:58 UTC, at a depth of 11.7 km (shallow). USGS received 2 “Did You Feel It?” reports, with a maximum reported intensity of II (weak).
- Magnitude
- 3.9
- Minor · ml
- Depth
- 12 km
- Shallow
- Felt reports
- 2
- Max intensity II
- Est. shaking
- IV
- Light (ShakeMap)
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 50 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
11 tons of TNT
That is about 1/1,410 of the Hiroshima bomb. A magnitude 5.0 releases about 45 times more energy.
Tectonic setting
134 km
from the nearest mapped plate boundary, between the North American and Pacific plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.
Depth: shallow
12 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
Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.
| Place | Intensity | Reports | Distance |
|---|---|---|---|
| 99685<br>0.320 | II · Weak | 2 | 494 km |
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 50 km
USGS lists 4 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M2.9 on October 19, 2024. 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 328 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.6The 1946 Unimak Island, Alaska EarthquakeApril 1, 1946 · 286 km SW of this epicenter
- 8.21938 Semidi Islands, Alaska EarthquakeNovember 10, 1938 · 78 km E of this epicenter
- 8.22021 Chignik, Alaska EarthquakeJuly 29, 2021 · 100 km E of this epicenter
- 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 52 km E of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 59 km S of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 33 km SW of this epicenter
- 7.22023 Sand Point, Alaska EarthquakeJuly 16, 2023 · 118 km SW of this epicenter
- 7.190 km SE of King Cove, AlaskaMay 14, 1948 · 126 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 11 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 169 recorded deaths. The most severe:
- 1946M8.6
Unimak Island
1 Apr 1946 · 286 km away · intensity VI
168 deaths$26 million damagetsunami
- 2023M7.2
Alaska Peninsula
16 Jul 2023 · 113 km away · intensity VI
1 deathtsunami
- 2020M7.8
Alaska
22 Jul 2020 · 52 km away · intensity VII
Limited damage (under $1M)tsunami
- 1938M8.2
Alaska
10 Nov 1938 · 77 km away · intensity VI
tsunami
- 2021M8.2
Alaska Peninsula
29 Jul 2021 · 102 km away · intensity VIII
tsunami
- 1788M8.0
Alaska Peninsula
6 Aug 1788 · 102 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.