M7.8 earthquake 2020 Perryville, Alaska Earthquake

Wednesday, July 22, 2020, 06:12:44 UTC · 55.072°N, 158.596°W

A magnitude 7.8 earthquake struck 2020 Perryville, Alaska Earthquake on Wednesday, July 22, 2020, 06:12:44 UTC, at a depth of 28.0 km (shallow). USGS received 195 “Did You Feel It?” reports, with a maximum reported intensity of IX (violent). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M8.2 on November 10, 1938.

Tsunami flagUSGS sets this flag for large events in oceanic regions so tsunami warning centers review them. It does not by itself mean a tsunami occurred. Check tsunami.gov and local authorities for official messages.

Magnitude: 7.8; Major · mww
Depth: 28 km; Shallow
Felt reports: 195; Max intensity IX
Est. shaking: VII; Very strong (ShakeMap)
PAGER alert: Green; Impact estimate
Tsunami: Flag; Check tsunami.gov

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

7.6 megatons of TNT

That is about 502 times the Hiroshima bomb. It released about 15,849 times the energy of a magnitude 5.0.

Tectonic setting

114 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

28 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
99603<br>0.199	III · Weak	20	668 km
99628<br>0.224	III · Weak	15	427 km
99661<br>0.269	VII · Very strong	8	134 km
99670<br>0.269	III · Weak	8	416 km
99613<br>0.277	IV · Light	7	428 km
99615<br>0.277	II · Weak	7	427 km
99648<br>0.285	VII · Very strong	6	107 km
99502<br>0.285	II · Weak	6	845 km
99669<br>0.285	II · Weak	6	748 km
99672<br>0.285	II · Weak	6	766 km
99612<br>0.293	VI · Strong	5	216 km
99559<br>0.293	II · Weak	5	669 km

I felt it — report to USGS ↗

USGS PAGER estimate

Who was exposed to shaking

Modelled from the ShakeMap and population data. Alert level green: low likelihood of casualties and damage.

IV · Light shaking: 1,200 people

Estimated shaking in nearby towns

Sand PointPopulation 976IV · Light

After the main event

Aftershocks within 200 km

USGS lists 455 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.1 on July 28, 2020. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 253 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 8 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

2020M7.8
Alaska
22 Jul 2020 · 0 km away · intensity VII
Limited damage (under $1M)tsunami
1938M8.2
Alaska
10 Nov 1938 · 48 km away · intensity VI
tsunami
1788M8.0
Alaska Peninsula
6 Aug 1788 · 153 km away
tsunami
2020M7.6
Alaska
19 Oct 2020 · 84 km away · intensity IX
tsunami
1948M7.5
Alaska Peninsula
14 May 1948 · 167 km away
1989M6.9
Alaska
4 Sep 1989 · 123 km away
tsunami

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

Nearby trackers