A Generalized H-κ Method With Harmonic Corrections on Ps and Its Crustal Multiples in Receiver Functions

The H-κ method (Zhu & Kanamori, 2000, https://doi.org/10.1029/1999JB900322) has been widely used to estimate the crustal thickness (H) and the ratio of P to S velocities (V_P/V_S ratio, κ) with receiver functions. However, in regions where the crustal structure is complicated, the method may produce biased results, arising particularly from dipping Moho and/or crustal anisotropy. H-κ stacking in case of azimuthal or radial anisotropy with flat Moho has been proposed but not for cases with plunging anisotropy and dipping Moho. Here we propose a generalized H-κ method called H-κ-c, which corrects for these effects first before stacking. We consider rather general cases, including plunging anisotropy and dipping interfaces of multiple layers, and use harmonic functions to correct for arrival time variations of Ps and its crustal multiples with back azimuth (θ). Systematic synthetic tests show that the arrival time variations can be well fitted by cosθ and cos2θ functions even for very complex crustal structures. Correcting for the back azimuthal variations significantly enhances H-κ stacking. We verify the feasibility of the H-κ-c method by applying it to 40 permanent stations in various geological setting across the Mainland China. The results show clear improvement after the harmonic corrections, with clearer multiples and stronger stacking energy, as well as more reliable H-κ values. Large differences in H (up to 5.0 km) and κ (up to 0.09) between the new and traditional methods occur mostly in mountainous regions, where the crustal structure tends to be more complex. We caution in particular about systematic bias when the traditional method is used in the presence of dipping interfaces. The modified method is simple and applicable anywhere in the world.