Body-wave extraction and tomography at Long Beach, CA, with ambient-noise interferometry

We retrieve diving P waves by applying seismic interferometry to ambient noise records observed at Long Beach, California, and invert travel times of these waves to estimate 3D P-wave velocity structure. The ambient noise is recorded by a dense and large network, which has about 2500 receivers with 100-m spacing. In contrast from the surface-wave extraction, body-wave extraction is much harder because body-wave energy is less than surface waves in this scale. For travel-time tomog-raphy, we need to extract body waves at each pair of receivers separately. Therefore, we employ two post-correlation filters to reject noisy signals (which are unusable for body-wave to-mography). The first filter rejects traces base on low P-wave correlation with the stack of all traces at that distance. The sec-ond filter measures coherent energy between all retained traces and suppresses incoherent noise in each trace. With these fil-ters, we can reconstruct clear body waves from each virtual source. Then we estimate 3D P-wave velocities from these waves with travel-time tomography. The velocities show high resolution structure