Multi‐Scale Seismic Imaging of the Ridgecrest, CA, Region With Waveform Inversion of Regional and Dense Array Data

We develop an inversion procedure for deriving multi‐scale velocity models with waveform inversions of earthquake and ambient noise data at multi‐frequency bands recorded by regional and dense sensor configurations. The method is applied for the area around the 2019 Ridgecrest earthquake rupture zones, utilizing data recorded by regional stations and dense 2D and 1D arrays with station spacings of ∼5 km and ∼100 m, respectively. Starting with regional Vp, Vs models and locations of Ridgecrest aftershocks, the velocity models and event locations are improved iteratively by inversions of waveforms recorded by regional stations and the 2D array, using a minimum spectral element size of ∼600 m. Waveforms from local events recorded by dense 1D arrays across the M7.1 rupture zone with frequencies of up to 10 Hz are used to resolve small‐scale features of the rupture zone and shallow crust with a local spectral element size of 80 m. The refined models provide self‐consistent descriptions of the rupture zone and the shallow crust embedded in the regional structures. The results reveal pronounced low Vs and high Vp/Vs in the M6.4 and M7.1 rupture zones coinciding with concentrations of seismicity, and also around the Garlock fault and in several local basins. We also observe clear velocity contrasts across the Garlock fault with polarity reversals along strike and with depth. The obtained multi‐scale velocity models can be used to improve derivations of earthquake source properties, simulations of dynamic ruptures and ground motions, and the understanding of fault and tectonic processes in the region. Plain Language Summary Seismic velocity models are foundational for a wide range of topics including clarifying properties of subsurface and fault zone structures, derivation of earthquake source properties, and simulations of ruptures and seismic ground motions. Typical imaging studies are done at given spatial scales and resolutions related to the used seismic network. Here we develop a methodology for multi‐scale multi‐resolution tomographic waveform imaging using data recorded by regional and local denser seismic networks. Application of the methodology to seismograms recorded in the region around the 2019 Ridgecrest earthquake sequence provide detailed information about seismic velocities in the main earthquake rupture zones and the shallow crust, embedded within a regional context. The results highlight anomalous ratios of P‐to‐S wave velocities in the rupture z