PandSreceiver function analysis of seafloor borehole broadband seismic data

Abstract

[1] The crustal and lithospheric structure of the normal oceanic plates is investigated using converted wave techniques (P and S receiver functions (RFs) and novel stacking analysis techniques without deconvolution) applied to the data from two seafloor borehole broadband seismic stations located in the central Philippine Sea and in the northwest Pacific ocean. We observe sufficient energy from at least two discontinuities within the error bounds, one from the crust-mantle (Moho) boundary and the other from the seismic lithosphere-asthenosphere boundary (LAB). Synthetic seismograms for seafloor stations show that the water reverberations interfere with the vertical component of seismograms but to a lesser extent with the radial part of P receiver functions. On the other hand, S receiver functions are devoid of such effects since all the multiples and converted waves are separated in time by the primary S wave in time. Waveform modeling of RFs shows that the crustal thicknesses of the western Philippine Sea plate and northwest Pacific plate are ∼7–8 km, and that depths of LAB are 76 ± 1.8 km and 82 ± 4.4 km, respectively, with an abrupt Vs drop at LAB of ∼7%–8%, as reported by Kawakatsu et al. (2009). The LAB depth for the eastern Philippine plate is found to be ∼55 km. To confirm the robustness of this observation, we further analyze vertical and radial components of the data without deconvolution for P wave backscattered reflection phases and P-to-S converted phases. The result indicates that the reflected/converted phases from Moho and LAB are observed at timings consistent with the receiver function results. The effect of seismic anisotropy for observed RFs is also investigated.