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Determine crustal thickness and velocities by using receiver functions and PmP travel times

Crustal thickness (H) and Vp/Vs ratio (κ) are two important parameters in characterizing a crustal structure. Their estimates from receiver function data often have large uncertainties due to a severe trade-off between the two parameters when the receiver functions only have the Moho P-to-S converted phase and its crustal multiples are weak or missing, which are common in tectonically active regions. Here, we extend the H-κ stacking method by combining receiver functions and PmP travel times to determine H, κ, and Vp simultaneously. We developed a deconvolution technique to measure PmP travel times using the post-critical Moho P-wave reflection SsPmp in the teleseismic S wave. Synthetic tests show that the new methods can reliably extract the PmP travel times and determine crustal thickness and velocities as long as the Moho Ps is clear in receiver functions. We applied the methods to 63 broadband seismic stations in the western Hubei Province of China. The results confirm the rapid increase of crustal thickness revealed in a previous study from the low-elevation plains in the eastern part of the study area to the high-rise mountains in the west. The corresponding increase of crustal Poisson’s ratio from low-to-intermediate values to intermediate-to-high values suggests that the crust in the eastern part is more felsic, most likely due to delamination of a portion of the mafic lower crust of the Yangtze platform in the Late Mesozoic.