YQ (2024-2025): Lake basin seismic response measurements for Lake Skilak, Alaska

• United States Geological Survey (USGS), United States of America

The goal of this experiment is to measure ground motion amplification and tuning of earthquake arrivals using ocean bottom seismographs (OBS) and onshore seismographs deployed in and around Skilak Lake, which is on the Kenai Peninsula, Alaska. Shaking by earthquakes can trigger turbidite flows in lakes, which provide a detailed paleoseismic record of past earthquakes. Earthquake-triggered lacustrine turbidite flows have been observed directly with turbidity sensors during recent earthquakes and as turbidite deposits in sediment cores. The core records often contain annual and semi-annual variations (e.g., varves) that can be used to determine precise dates for the past events. Translating detailed lacustrine turbidite records into earthquake recurrence histories requires knowing how susceptible lake-bottom sediments are to shaking during earthquakes and tuning and amplification effects of the lake basin itself. Since lake-basin shape, depth, and orientation affect ground motion amplification and frequency content, certain lakes are likely more or less sensitive to certain types of earthquakes (e.g., megathrust vs upper plate). Models of ground motion susceptibility in specific lake basins can be used to associate source sizes and types with the turbidite record. For the Lake Skilak project, we will deploy two OBS equipped with either Guralp CMT-3T or Trillium Compact sensors on the lake bottom for ~12 months. The OBS will come from the Woods Hole Oceanographic Institution. Measuring lake basin response requires reference sites. Permanent station AK.SLK will provide one of these reference sites. We would like to also install 4 on-shore stations near the lake shore using PASSCAL broadband sensors to provide additional reference sites and improve azimuthal coverage. Possible sensors for these include Guralp CMT-3T, Trillium 240s or similar, but I'd like to discuss the sensor and station design with PASSCAL.

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