Calibrating Alaska’s natural seismograph: preliminary results of the sedimentary response to strong ground motion in south-central Alaska’s lakes and fjords
Drake Singleton
USGS
- Date & Time
- Location
- Online-only seminar via Microsoft Teams
- Summary
South-central Alaska is a region of high seismicity that is frequently impacted by intraslab earthquakes. Intraslab earthquakes, which occur at mid-crustal depths, do not produce the characteristic surficial faulting, land-level change, or tsunami deposits typically associated with megathrust earthquakes, but instead generate a more subtle signal in the geologic record. The emerging field of lacustrine and fjord paleoseismology utilizes relatively small and well-defined basins with unique depositional characteristics (e.g., varve formation), in combination with earthquake-generated turbidity deposits as paleoseismic proxies, to construct earthquake histories that are sensitive enough to record intraslab events. The 2018 Anchorage Earthquake resulted in high-intensity shaking across the upper Cook Inlet and highlighted the region’s vulnerability to intraslab earthquakes. Recent work on Eklutna Lake by Van Daele et al. (2020) has confirmed the presence of earthquake-generated turbidites as a result of the 2018 earthquake across the lake’s two sub-basins. The results of their study provided some of first inputs necessary to begin calibrating south-central Alaska’s natural seismograph. However, important questions remain, including the minimum MMI necessary to trigger turbidity currents, which depositional environments are most susceptible to failure by seismic triggers, and the potential of relative turbidite thickness as an indicator of epicentral direction. I’ll present preliminary results from fieldwork carried out this summer 2020 in south-central Alaska that focused on the collection of short-barrel gravity cores, MCS Sparker profiles, and high-resolution Chirp data. The goal of this project will be to characterize the sedimentary response of south-central Alaska’s lakes and fjords to the 2018 Anchorage Earthquake. As a first step, short-barrel gravity cores are used to investigate the spatial extent of turbidity currents triggered by the 2018 Anchorage Earthquake, and if possible, identify a correlating acoustic signature.
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