Reviewed by USGSAlaska4y ago
M4.5 earthquake 151 km SSW of Akhiok, Alaska
Monday, November 15, 2021, 09:19:13 UTC · 55.803°N, 155.514°W
A magnitude 4.5 earthquake struck 151 km SSW of Akhiok, Alaska on Monday, November 15, 2021, 09:19:13 UTC, at a depth of 8.5 km (shallow). USGS received 2 “Did You Feel It?” reports, with a maximum reported intensity of II (weak). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M5.6 on October 31, 2021.
- Magnitude
- 4.5
- Light · ml
- Depth
- 9 km
- Shallow
- Felt reports
- 2
- Max intensity II
- Est. shaking
- IV
- Light (ShakeMap)
- PAGER alert
- Green
- Impact estimate
- 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
85 tons of TNT
That is about 1/178 of the Hiroshima bomb. A magnitude 5.0 releases about 6 times more energy.
Tectonic setting
101 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
9 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 |
|---|---|---|---|
| 99615<br>0.320 | II · Weak | 2 | 234 km |
USGS PAGER estimate
Who was exposed to shaking
USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No populated area was estimated to feel noticeable shaking.
After the main event
Aftershocks within 50 km
USGS lists 1 M2.5+ earthquake within 50 km in the following 30 days; the largest was M4.1 on December 6, 2021. 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 384 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.21938 Semidi Islands, Alaska EarthquakeNovember 10, 1938 · 182 km W of this epicenter
- 8.22021 Chignik, Alaska EarthquakeJuly 29, 2021 · 157 km W of this epicenter
- 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 211 km W of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 293 km SW of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 290 km W of this epicenter
- 7.14 km ENE of Karluk, AlaskaNovember 7, 1912 · 210 km N of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 79 km W of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 13 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1900M8.3
Kodiak Island
9 Oct 1900 · 190 km away · intensity VIII
Limited damage (under $1M)
- 1788M8.0
Unga Island
21 Jul 1788 · 204 km away · intensity VII
Limited damage (under $1M)tsunami
- 2020M7.8
Alaska
22 Jul 2020 · 211 km away · intensity VII
Limited damage (under $1M)tsunami
- 1970M6.0
Andreanof Islands
11 Mar 1970 · 213 km away · intensity V
Limited damage (under $1M)tsunami
- 1792
Kodiak Island
1792 · 254 km away · intensity VII
Limited damage (under $1M)tsunami
- 1938M8.2
Alaska
10 Nov 1938 · 183 km away · intensity VI
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.