Campaign GPS Deployments

Weather in Chignik has been spectacular so far, but internet is amazingly slow. All things considered, that’s a good tradeoff. But it means the photos may be low-res…

Yesterday we set out all 7 of the campaign GPS sites in the Chignik area. We set up the GPS antenna on a tripod over the survey marker, and will leave it to record for a couple of days, then pick it up. That gives us the post-earthquake position, and we know the pre-earthquake position from its last survey (2016), and its velocity. After making some small corrections for several earthquakes (Kodiak/Gulf of Alaska 2018, plus the two 2020 Shumagin earthquakes), we’ll get a precise measurement of the coseismic displacements plus the first 2-3 weeks of afterslip. The figure shows predicted displacements from the USGS finite fault model, with the black vectors being the permanent NOTA/PBO sites, and the green vectors being the campaign GPS sites.

Planned observation sites, with the epicenter (red star) and approximate rupture area (box). Displacement vectors are predictions from the USGS finite fault model. Black: Network of the Americas (NOTA) continuous sites. Green: campaign survey sites. Blue vectors show observations that will be expected from Jeff Freymueller’s Simeonof earthquake project in the Shumagin islands. Yellow dots are planned 1-year seismic station deployments; the Chowiet site also will have continuous GPS. The red dots are the other continuous GPS site locations.

Right now it looks like the weather is going to remain outstanding through Friday, but likely will get bad late Friday. Then we will likely get rain and fog over the weekend, so we hope to finish all the work here before we get socked in, then head to Sand Point.

Today we are building the first two continuous sites out in the Semidi islands, which will be just a few meters away from the campaign sites but will be left to record a continuous record of afterslip and viscoelastic relaxation for the next year. We will also have to collect all of the campaign sites before the weather gets bad, so that we get the data. Otherwise, the instruments will be stranded out until next year, which would not be good at all.

Our plans after that depend on how long those site installs turn out to take. We also have two more campaign sites to set up that are in between here and Sand Point, but we will end up picking those up later out of Sand Point.

Jeff Freymueller, Michigan State University

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