The Alaska Amphibious Community Seismic Experiment was sited along the Alaska Peninsula for several reasons, but one of those was the potential for a large earthquake there. Now, since July 2020, there have been three, with the latest and largest being the M8.2 Chignik earthquake on July 29, 2021 (more info at the Alaska Earthquake Center). The National Science Foundation (NSF) is supporting a rapid field response to this earthquake, and we Jeff/Geoffs are leading the temporary deployment component of that, with many participants set to do critical work in the coming few weeks, and with crucial support from the NSF GAGE and SAGE facilities (operated by UNAVCO and IRIS). In parallel, GAGE/UNAVCO is rapidly fixing failed communications at several Network of the Americas (NOTA) sites close to the earthquake.
Our team will be posting field updates, daily if possible, to this blog and we’re counting on UNAVCO and IRIS (and you!) to help spread the word around! Internet connectivity for the field teams will often be marginal, but we’ll get as much out as we can.
What do we know about the earthquake so far? The earthquake hypocenter (where it started) was at about 30 km/20 miles depth offshore of the town of Perryville, Alaska. Big earthquakes like this rupture over a large area, and this one continued to the northeast for about 100 km/50 miles, ending near a small island group called the Semidi Islands. The Alaska Maritime National Wildlife Refuge has two biology field technicians living and working on one of those islands for the summer, and their Facebook page has a series of posts detailing their experiences and observations of the earthquake and its effects. Check it out!
Our field response is focused on collecting critical new data from as close to the earthquake rupture as possible, so that our scientific community has the data to study the earthquake and its after-effects in as much detail as possible. We want to know the detailed geometry of the fault that ruptured, how much slip happened on the fault and where, and how that relates to the pattern of fault creep (and frictionally stuck parts of the fault) in the time before and after the earthquake. We’ll be going to the Semidi Islands and other places around the earthquake rupture, surveying benchmarks to measure earthquake displacements, installing temporary seismometers to record aftershocks, and installing some continuous GPS sites to record postseismic movements. We will get data for the earthquake displacements within the next few weeks, and next summer we will get a huge trove of new data when we download or remove the temporary instruments.
Our seismological field team is en route to Kodiak right now, and will start putting in seismometers to record until next summer within the next couple of days. Over the coming weeks, we’ll have posts from our seismology and GPS field teams, and from UNAVCO’s GAGE facility engineers.
Jeff Freymueller, Michigan State University, and Geoff Abers, Cornell University