P-SV MULTIMODE SUMMATION DIFFERENTIAL SEISMOGRAMS FOR LAYERED STRUCTURES

We present a fast and accurate analytical method for computing differe ntial seismograms with respect to structural model parameters. The met hod adopts the P-SV-wave multimode summation formalism for laterally h omogeneous layered media. The differential seismograms calculated anal ytically do not suffer from the numerical noise and instability affect ing numerical calculations. The frequency range for application of the method spans from regional-scale seismology to seismic engineering. C omputationally, the proposed analytical method is equivalent to determ ining two-mode spectra. In contrast to NS-l (or 2N) mode spectra for a typical 'brute-force' numerical finite difference approach, the metho d reduces the computations to 2/(N + 1) (if a one-sided perturbation f inite difference scheme is used), which corresponds to a 90 per cent s aving for 20 (N = 20) layers. The speed and accuracy of the technique make it extremely attractive for structural parameter waveform inversi ons.