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.

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.

Stations Downloaded

Station	Distance (km)	1 Hz	5 Hz
AB13	117	X
AC12	124	X
AC28	143	X
AB07	167	X
AC41	174	X
AC40	185	X
AC25	286	X
AC42	331	X
AC34	353	X	X
AC26	393	X
AB14	428	X
AC67	431	X
AC08	475	X
AC27	490	X
AC39	493	X
AV02	519	X	X
AV20	521	X
AV01	521	X
AV16	521	X
AV04	522	X
AV18	523	X
AC18	525	X
AV17	525	X
AV09	585	X	X
SELD	588	X	X
AC03	610	X	X
AC47	614	X
AC37	616	X
AC06	646	X
AC17	675	X
AC23	706	X
AC15	748	X
AB08	750	X
AC36	757	X
AB02	765	X
AC51	771	X
AC20	799	X
AC32	800	X
AB28	808	X
PMKZ	809	X	X
FS63	832	X	X
FS82	836	X	X
AC19	837	X
AC14	844	X
WAAK	846	X	X
AC53	847	X
STEM	852	X	X
AC48	857	X	X
ATW2	862	X	X
AC11	908	X	X
AT01	939	X	X
AB17	967	X
AC75	974	X
WIKR	996	X
AC74	1040	X
AB35	1059	X
GRNX	1070	X
AC77	1083	X
AC64	1128	X
AC71	1184	X
AC50	1197	X
CLGO	1197	X
AC07	1200	X
AC78	1246	X	X
AB09	1273	X
AC61	1308	X
AB43	1329	X	X
AB33	1389	X
AB39	1421	X
AB50	1454	X
TLK2	1541	X
AB51	1553	X
AB53	1558	X
AB49	1559	X
AB45	1565	X
SG27	1784	X	X
BARO	1784	X	X
P401	2419	X	X
P816	2419	X	X
P403	2438	X	X
P402	2445	X	X
P435	2479	X	X
P439	2479	X	X
SC02	2482	X	X
PABH	2485	X	X
P400	2492	X	X
P436	2503	X	X
P399	2509	X	X
P438	2510	X	X
P398	2521	X	X
P419	2526	X	X
EYAC		X
AC21		X
AC35	619	X
AB15	648	X
AC79	810	X	X
AC44	817	X
AC80	861	X
AC33	915	X
AC70	1043	X	partial
AC31	1066	X
AC62	1083	X
AC65	1160	X
AC76	1192	X
AB48	1452	X
P441	2516	X
AC13	150	X
AC45	267	X
AC02	291	X
AC24	381	X
AC38	387	X
AV19	522	X	X
AV11	525	X
AC52		X

Last update: 8/23/2021