Eikonal surface wave tomography with smoothing splines—application to Southern California

SUMMARY The densification of both permanent and temporary seismic networks has raised new interest in surface wave eikonal tomography from which phase velocity maps can be obtained without resolving a tomographic inverse problem. However, requires to reconstruct traveltime surfaces discrete number measurements at the station locations, challenging. We present method these with smoothing splines discretized regular 2-D Cartesian grid. impose Neumann boundary conditions so that gradients on edges grid are equal apparent slownesses average plane along normal direction measured by beamforming. Using equation, then derived norm gradient interpolated maps. is applied Rayleigh waves recorded Southern California Seismic Network derive surfaces. Robust, stable finely resolved 25 33 s period after averaging analysis selection recent large (Mw ≥ 6.5) teleseismic events. map mainly constrains thickness crust, results excellent agreement previous studies.