Investigating meter-scale wavefield complexity and amplification at the basin edge with a fiber-optic array

Edges of sedimentary basins generate complex seismic wavefield effects and localized amplification. Characterizing these effects and incorporating them into hazard models is difficult because tomographic models are often smooth and wavefield observations are often aliased. Distributed acoustic sensing (DAS) transforms telecommunication fibers into ultra-dense strainmeter arrays, enabling inferences of precise velocity structure, recordings of wavefields at the meter scale over large areas, and measurements of dynamic strain, a quantity with distinct implications for buried infrastructure. With a DAS array in Arcata, California, we resolve a fine-scale shallow velocity model and compare it to observed wavefields from local earthquakes. We find evidence for multiple basin edges and observe a spatial correlation between these features and locally scattered surface waves that amplify dynamic strain. Two-dimensional synthetic tests verify that sharp velocity contrasts at basin edges induce these waves and also illustrate how dynamic strain and ground velocity behave differently at these boundaries.