Probing the Seattle Basin Edge Using a Dense Urban Nodal Array in 100 Backyards

Abstract Sedimentary basins amplify seismic waves, particularly at basin edges where strong velocity contrasts lead to reflections, refractions, and diffractions. To better understand how the Seattle basin’s southern edge, the Seattle fault zone (SFZ), acts as a seismic boundary, we deployed 100 three-component nodal seismometers (Magseis Fairfield ZLand 3C) at ∼250 m spacing along four north–south transects across the SFZ for one month (13 July to 11 August 2019), recording ambient seismic noise and earthquakes at 500 Hz. The intent of this article is to introduce this data set, and showcase a diversity of preliminary analyses to that illustrate its rich potential, and encourage future deeper analyses. Preliminary ambient noise cross-correlations yield stable Green’s functions to 4 km interstation distance and average Rayleigh-wave phase velocities of ∼400 m/s, consistent with shallow VS30 models. We also resolve a diffracted wave across the Seattle basin edge and fault zone, and compute earthquake site-amplification metrics that indicate amplification factors of up to 39× in high-frequency bands. Along with our other preliminary results, these findings hint at substantial small-scale variability in velocity and amplification, underscoring the power of dense urban nodal arrays for localized seismic hazard assessment. Data and metadata are archived as Network Z6_2019 with the International Federation of Digital Seismograph Networks (Denolle and Toghramadjian, 2019), and processing scripts used for analysis in this article are available on GitHub.