Collaborative Research: RAPID: Response to the 29 July 2021 Chignik M8.2 Earthquake

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This RAPID award is a response to The July 2021 Chignik earthquake (M8.2) along the Alaskan Peninsula. This is the biggest earthquake in the US since 1965 (Rat Islands). It ruptured a segment of the megathrust offshore of the Alaska Peninsula, which last ruptured in 1938. The project deploys an integrated on-land observational field campaigns: geodesy to rapidly resurvey nearby monuments and document earthquake-related deformation, and seismology to deploy nearby instruments to record aftershocks. Understanding this earthquake will provide critical information for evaluating models of earthquake behavior and hence hazard among the planet’s largest earthquakes. Although only a small tsunami occurred, understanding better the rupture will allow for more realistic tsunami hazard assessments. The earthquake also provides ample opportunities for broadening participation in science, through rapidly making available data to the seismic and geodetic research communities. The project includes outreach to local schools, communities and governments and restarts a popular blog focused on geophysics in Alaska.The Chignik earthquake is a very rare example of a fault segment with two great earthquakes in the instrumental record, and is a critical locale to test theories of how seismic cycles work. The earthquake follows a pattern of along-strike segmentation previously documented between segments with large differences in locking behaviors and earthquake histories. The cause of this segmentation (or indeed of the variation in slip behavior more generally) remains uncertain, and collecting new data may elucidate the controlling mechanisms behind interseismic and coseismic rupture segmentation. Additionally, the earthquake provides an excellent laboratory to test theories of fault loading between segments and of our understanding of postseismic deformation. Almost precisely a year earlier, a M7.8 ruptured the abutting Shumagin segment to the west, indicating some possibility of triggering. That relationship can be explored, as well as the potential for bringing the next segment to the east closer to failure. The project takes advantage of decades of geodetic work on the Shumagins, Alaska Peninsula, and nearby islands, and the large 2018-9 GeoPRISMS-EarthScope-supported Alaska Amphibious Community Seismic Experiment. The project's outcome will be valuable in addressing questions related to the characteristics of earthquakes as articulated in the Earth in Time report from the National Academies of Science, Engineering and Medicine.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.