(a) Fréchet kernels of vertical-component Rayleigh wave traveltime (left panels) and amplitude (right panels) for P-wave speed α (top panels) and S-wave speed β (bottom panels) at a depth of 21 km. Waves with period of 25 s or longer are included. Also shown are cross-sections of the kernels within the source–receiver great-circle plane down to 150-km depth. In each cross-section plot, the dashed line indicates the Moho discontinuity. The source is at a depth of 21 km with a focal mechanism shown by the beachball. The receiver is on the surface at an epicentral distance of Δ= 19°. (b) Fréchet kernels of radial-component Rayleigh wave traveltime (left panels) and amplitude (right panels) for P-wave speed α (top panels) and S-wave speed β (bottom panels) at a depth of 21 km. Waves with period of 25 s or longer are included. The source is at a depth of 21 km with a focal mechanism shown by the beachball. The receiver is on the surface at an epicentral distance of Δ= 19°.