Speaker
Description
Accurate estimation of Newtonian Noise (NN) in gravitational wave observatories requires detailed knowledge of the seismic wavefield in the vicinity of the detector mirrors. This seismic wavefield is commonly obtained from numerical simulations at regional geological scale. These models are computationally demanding and typically rely on assumptions about the nature and location of seismic sources, for example through randomly distributed surface point loads, combined with fitting power spectral densities to field measurements.
In this contribution, we present an alternative methodology in which the seismic wavefield is reconstructed directly from measurements acquired by seismic arrays deployed in a region of interest (ROI) in the vicinity of the detector mirrors. It is assumed that the dynamic soil properties are known, whereas no prior information about the seismic sources is required. This eliminates the need for explicit source modeling or PSD fitting and allows for a computational domain restricted to the ROI. The wavefield reconstruction is formulated as a PDE constrained optimization problem that minimizes the misfit between measured and modeled seismic responses at the receiver locations. The reconstructed wavefield is subsequently used to assess wave scattering by the caverns, tunnels, and shafts of the underground infrastructure through a subdomain formulation and enables computationally efficient NN estimates.