M5.5 earthquake 123 km NNE of Atka, Alaska
A magnitude 5.5 earthquake struck 123 km NNE of Atka, Alaska on Tue, Oct 27, 2020, 7:13 PM HADT (04:13 UTC), 240 km (149 mi) below the surface.
Map
Where this earthquake was located, with the others nearby. Select one for its page.
The earthquake
- Magnitude
- 5.5 (mww), moderate
- Local time
- UTC
- 2020-10-28 04:13:42 UTC
- Depth
- 239.7 km (148.9 mi), intermediate-depth
- Epicenter
- 53.202° N, 173.416° W
- Region
- Alaska
- Strongest shaking
- III, weak shaking
- PAGER alert
- Green
- Tsunami flag
- Yes: a large quake in an oceanic region
- Status
- Reviewed by a seismologist
Tsunami
The USGS flags a quake this large in an oceanic region. The flag does not mean a tsunami happened; the tsunami warning centers decide that, and their messages are below when they issued any.
Current tsunami warnings: tsunami.gov. Warnings in force in the US also appear on our alerts pages.
Shaking
The USGS ShakeMap: shaking estimated from seismic stations and the quake’s size, on the Modified Mercalli intensity scale.
- Strongest estimated
- III, weak shaking
- Peak ground acceleration
- 0.2% of gravity
- Peak ground velocity
- -1.8 cm/s
- Map
- Automatic
Did you feel it?
No one has reported feeling this quake to the USGS.
Estimated impact
The USGS PAGER system estimates deaths and economic losses from the shaking and the population and buildings exposed to it.
- Alert level
- Green: little or no damage or loss of life expected
| Range | Chance |
|---|---|
| Under 1 | 69% |
| 1 to 10 | 29% |
| 10 to 100 | 2% |
| 100 to 1,000 | Under 1% |
| 1,000 to 10,000 | Under 1% |
| 10,000 to 100,000 | Under 1% |
| 100,000 to 10,000,000 | Under 1% |
| Range, million USD | Chance |
|---|---|
| Under 1 | 65% |
| 1 to 10 | 30% |
| 10 to 100 | 4% |
| 100 to 1,000 | Under 1% |
| 1,000 to 10,000 | Under 1% |
| 10,000 to 100,000 | Under 1% |
| 100,000 to 10,000,000 | Under 1% |
Fault motion and ground failure
How the rock slipped, from the moment tensor, and the USGS estimate of landslides and liquefaction.
- Faulting
- Strike-slip
- Moment magnitude
- 5.5 Mww
- Nodal plane 1
- Strike 196°, dip 30°, rake 10°
- Nodal plane 2
- Strike 97°, dip 85°, rake 120°
How well it is located
Reviewed by a seismologist.
- Location uncertainty
- About 6.8 km horizontally, 3.6 km in depth
- Magnitude uncertainty
- ±0.03
- Depth from
- From location
- Station coverage gap
- 50°
- Stations used
- 210
Nearby
Within 100 km, magnitude 2.5 and up: 6 in the 60 days after this one and 3 in the 30 days before it.
After
- 2.755 km NNW of Atka, Alaska · 2162 days ago · 183 km deep · 92 km away
- 4.3130 km ENE of Atka, Alaska · 2150 days ago · 138 km deep · 92 km away
- 2.933 km NNE of Atka, Alaska · 2148 days ago · 218 km deep · 91 km away
- 2.631 km N of Atka, Alaska · 2126 days ago · 170 km deep · 94 km away
- 4.562 km N of Atka, Alaska · 2117 days ago · 182 km deep · 68 km away
- 2.6144 km NE of Atka, Alaska · 2116 days ago · 145 km deep · 69 km away
Before
Earthquakes todayAlaska earthquakesLive radar here
Sources
From the USGS Earthquake Hazards Program and its partner networks, event us7000c6l2 (also filed as at00qiw92t, pt20302000, ak020dvirf4r, iscgem619509233). Read Wed, Sep 30, 2026, 10:22 AM UTC.