Left-hand side: N–S component synthetic seismogram computed using a spectral-element method (Fichtner & Igel 2008). The time window around the Love wave used to compute Fréchet and Hessian kernels is shaded in grey. The dominant period is 25 s. Right-hand side: Fréchet kernel for a cross-correlation time-shift measurement on the N–S component Love wave shown to the left-hand side. The source and receiver positions are marked by + and •, respectively.