Shallow Modeling and Site‐Amplification From Telecommunications Fibers in Istanbul

Abstract We use pre‐existing fiber‐optic telecommunications fibers in Istanbul, Türkiye, to generate a seismic velocity model of the subsurface down to 100 m depth, and estimate site‐amplification in the region. We collect ambient noise, predominantly from urban traffic, along the 8 km segment fiber, extract Rayleigh wave dispersion curves, and use a trans‐dimensional Monte‐Carlo algorithm to estimate shear wave velocities along the profile that is consistent with local expectations of geology. We then estimate site‐amplification in three different ways: (a) using 1D estimates drawn from the velocity model, (b) through 2D earthquake simulations across the model and (c) by comparing to real earthquake data, which were dominated by the Kahramanmaraş sequence in 2023. All three estimates of site response roughly agree in both spatial distribution and amplification factor, and the study demonstrates the efficacy of using telecommunications fibers in urban environments for seismic hazard estimates.