Surface-wave phase-velocity models of the United States: Expanding with USArray coverage

Wednesday, 17 December 2014
Anna E Foster, Earth Observatory of Singapore, Singapore, Singapore, Goran Ekstrom, Lamont-Doherty Earth Observ, Palisades, NY, United States and Meredith Nettles, Columbia Univ, Palisades, NY, United States
We update our models of Love and Rayleigh wave phase-velocity structure using USArray data through mid 2014. We make measurements of the phase at periods from 25 to 100 s using a two-station method that assumes a great-circle arrival path for Love waves, and uses the estimated arrival angle for Rayleigh waves to correct the two-station calculation. Arrival-angle estimates are made with a mini-array method that employs a grid search to select the back-azimuth to the source that best predicts the phase observed on a local subset of stations. The two-station phase data with inter-station path lengths between 350 and 750 km are inverted to produce phase-velocity models at discrete periods. The new data set expands the modeled area, covering the entire contiguous United States.

The mini-array method also produces an estimate of the local phase-velocity. We calculate this local phase-velocity for both Love and Rayleigh waves, and compare the measurements with the maps resulting from the inversion of the two-station measurements. The local phase velocities, two-station phase velocities, and two-station phase-velocity models are all examined for bias resulting from overtone interference. Based on previous work, we expect overtone interference to affect Love wave measurements but not Rayleigh wave measurements, and to affect the local measurements more than the two-station models.