GAGE Facility Response to the M8.2 Chignik Earthquake

The largest earthquake within US territory in the last 50 years occurred near Chignik, AK on July 28, 2021 at 22:15 local time. The NSF-funded GAGE Facility response to the M8.2 Chignik earthquake started within hours of the event. UNAVCO staff were mobilized to initiate high-rate data downloads from existing Network of the Americas (NOTA) cGNSS stations within 1000 km of the epicenter, which was located 104 km SE of Perryville, AK. An event response page was established immediately to provide a clearinghouse for all NOTA data and community science products. Predicted coseismic displacements, based on the USGS finite fault model were ~40 cm in the region proximal to the epicenter. Of the 117 NOTA GNSS stations in Alaska, 89 were fully operational, while 28 stations were experiencing telecommunications or other problems, which would require station visits within ~20 days to avoid high-rate GNSS data loss. Five of these non-operational stations were considered critical for immediate repair, given their proximity to the epicenter. This event response included the collection of GNSS data (daily files and 1 Hz observations) from as many NOTA GNSS stations as possible and the effort to make these data available to the community. UNAVCO PI project support staff worked with community PIs to support a NSF RAPID deployment of 7 temporary GNSS and 3 seismic stations as well as occupy existing campaign benchmarks within ~200 km of the main shock near Chignik, AK and in the Semidi and Shumagin Islands. The effort required considerable logistical and mission planning because of the remote Aleutian location, which required helicopter support to achieve the mission objectives, long-lead times for shipping gear and instruments from Boulder, CO and Anchorage, AK, and the possibility of inclement weather. We will report the results of the GAGE Facility support for this event.