Waveform Tomography Improves Far-Regional Distance Simulations of Underground Nuclear Explosions and Earthquakes from the Former Nuclear Test Site, Western United States

We investigated the efficacy of seismic Earth models to simulate complete regional distance waveforms from underground nuclear explosions and earthquakes on and near the former Nevada Test Site in Nevada, western United States. We focused on two far-regional stations (∼1000 km) in two period bands 20–50 and 15–40 s, for which path propagation effects over many wavelengths accumulate and pose challenges to low-mag-nitude nuclear explosion monitoring (NEM). Four seismic models were considered: two average radially symmetric 1D and two fully 3D models. Model performance was evaluated with metrics of waveform phase (cross-correlation delay time), shape (correlation coefficient), and amplitude (variance reduction with delay time shift) and averaged into a summary score. We found that a recent 3D model based on full waveform inversion (FWI) tomography including radial anisotropy and crustal thickness variations performs on average better than the alternatives. Results suggest that FWI based on crustal depth earthquakes can provide useful 3D models for NEM. Such models can be used for the simulation of Green’s functions for source characterization including moment tensor inversion and source type characterization (e.g., explosion–earthquake–collapse identification, moment and yield estimation).