Absolute S ‐velocity estimation from receiver functions

SUMMARY We present a novel method to recover absolute S velocities from receiver functions. For a homogeneous half‐space the S velocity can be calculated from the horizontal slowness and the angle of surface particle motion for an incident P wave. Generally, the calculated S velocity is an apparent half‐space value which depends on model inhomogeneity and P ‐waveform. We therefore, suggest to calculate such apparent half‐space S velocities from low‐pass filtered (smoothed) receiver functions using a suite of filter‐parameters, T . The use of receiver functions neutralize the influence of the P ‐waveform, and the successive low‐pass filterings emphasize the variation of S velocity with depth. We apply this V S ,app. ( T ) technique to teleseismic data from three stations: FUR, BFO and SUM, situated on thick sediments, bedrock and the Greenland ice cap, respectively. The observed V S ,app. ( T ) curves indicate the absolute S velocities from the near surface to the uppermost mantle beneath each station, clearly revealing the different geological environments. Application of linearized, iterative inversion quantify these observations into V S ( z ) models, practically independent of the S ‐velocity starting model. The obtained models show high consistency with independent geoscientific results. These cases provide also a general validation of the V S ,app. ( T ) method. We propose the computation of V S ,app. ( T ) curves for individual three‐component broad‐band stations, both for direct indication of the S velocities and for inverse modelling.