July 28, 2021 M 8.2 Alaska Earthquake

Event response pages are a service to help coordinate community science after an earthquake or other notable geophysical event by collecting relevant data. Findings and figures are preliminary and subject to revision.

At 6:15:47 (UTC) on July 28, a magnitude 8.2 earthquake occurred southeast of Perryville and Chignik, off the coast of the Alaska Peninsula. The event occurred within the footprint of the Network of the Americas (NOTA), a network of continuous GPS/GNSS stations and borehole instruments operated by UNAVCO that monitors plate motion and transient deformation, in addition to other applications. For more information about the earthquake, see the USGS Earthquake Hazards Program event page and the Alaska Earthquake Center news post.

UNAVCO is coordinating a response with community Principal Investigators to recover high-rate data from permanent stations and recent campaign instruments as quickly as possible. You can read more on the project’s blog. This page will be continually updated as that work proceeds, so please check back or follow us on Twitter or Facebook for updates.

Geologic Context

This earthquake occurred at the boundary where the Pacific plate meets and dives beneath the North American plate. As the plates overcame the friction locking them together and slipped, the North American plate moved upwards and towards the southeast. Such events can produce extremely dangerous tsunamis as the seafloor displaces the water above, and the Tsunami Warning Center immediately issued a tsunami warning. However, the resulting tsunami was small—less than a foot at locations in Alaska—and the warning was canceled after several hours.

map of GPS station vectors and plate boundary
GPS station velocities (averages, not during the earthquake) and the plate boundary that marks the Aleutian Trench.

The location of the July 29 earthquake was similar to the July 22, 2020 magnitude 7.8 Simeonof earthquake. During an earthquake, a patch of the fault plane slips, relieving accumulated strain. But this can load the boundaries of the patch with extra stress—which is often where aftershocks occur.

map showing main quakes and aftershocks for both this and last year's events
Image: Alaska Earthquake Center

Stations Downloaded


StationDistance (km)1 Hz5 Hz
AB13117X
AC12124X
AC28143X
AB07167X
AC41174X
AC40185X
AC25286X
AC42331X
AC34353XX
AC26393X
AB14428X
AC67431X
AC08475X
AC27490X
AC39493X
AV02519XX
AV20521X
AV01521X
AV16521X
AV04522X
AV18523X
AC18525X
AV17525X
AV09585XX
SELD588XX
AC03610XX
AC47614X
AC37616X
AC06646X
AC17675X
AC23706X
AC15748X
AB08750X
AC36757X
AB02765X
AC51771X
AC20799X
AC32800X
AB28808X
PMKZ809XX
FS63832XX
FS82836XX
AC19837X
AC14844X
WAAK846XX
AC53847X
STEM852XX
AC48857XX
ATW2862XX
AC11908XX
AT01939XX
AB17967X
AC75974X
WIKR996X
AC741040X
AB351059X
GRNX1070X
AC771083X
AC641128X
AC711184X
AC501197X
CLGO1197X
AC071200X
AC781246XX
AB091273X
AC611308X
AB431329XX
AB331389X
AB391421X
AB501454X
TLK21541X
AB511553X
AB531558X
AB491559X
AB451565X
SG271784XX
BARO1784XX
P4012419XX
P8162419XX
P4032438XX
P4022445XX
P4352479XX
P4392479XX
SC022482XX
PABH2485XX
P4002492XX
P4362503XX
P3992509XX
P4382510XX
P3982521XX
P4192526XX
EYACX
AC21X
AC35619X
AB15648X
AC79810XX
AC44817X
AC80861X
AC33915X
AC701043Xpartial
AC311066X
AC621083X
AC651160X
AC761192X
AB481452X
P4412516X
AC13150X
AC45267X
AC02291X
AC24381X
AC38387X
AV19522XX
AV11525X
AC52X
Last update: 8/23/2021

Did you feel it?

The USGS collects information from people who felt an earthquake and creates maps that show what people experienced and the extent of the damage

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Written by:

  • Scott K. Johnson
  • Posted: 29 July 2021
  • Last updated: 30 August 2021

Did you feel it?

The USGS collects information from people who felt an earthquake and creates maps that show what people experienced and the extent of the damage

Submit a response

Response Data

Please contact archive-gps@unavco.org for information on data availability. To request access to these and other RT-GPS stations operated by UNAVCO please send an email request to rtgps@unavco.org.

NOTA GPS/GNSS Data

Standard and high-rate data can be accessed via the Data Archive Interface. See above for information on data availability.

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Borehole Strain Data

High-rate data from borehole strainmeters can be accessed here.

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