Long-period body wave traveltimes through the crust: implication for crustal corrections and seismic tomography

The traveltimes of P and SH waves through the crust depend strongly on wave period. At periods longer than 10-15 s, where traveltime measurements for indirect (e.g. surface reflected and core reflected) waves are typically made, the traveltimes are shorter than predicted by ray theory. Crustal corrections, often used in global mantle tomography to isolate the effects of the crust on teleseismic traveltimes, may have a complex frequency dependence and influence finite-frequency inversions. Crustal corrections for profiles of CRUST2.0 and the PREM reference model for the mantle may be several seconds larger or smaller than ray-theoretical values, depending on crustal thickness, crustal velocities and wave period. This variability is observed in the difference times between the seismic phases SS and S and between PP and P. It is therefore important to incorporate the effects of the crust on traveltimes in finite-frequency tomography, in order to take full advantage of the variable mantle sensitivity of body waves at different periods.