Receiver Function Investigations of Seismic Anisotropy Layering Beneath Southern California

Abstract

Seismic azimuthal anisotropy characterized by shear wave splitting analyses using teleseismic XKS phases (including SKS, SKKS, and PKS) is widely employed to constrain the deformation field in the Earth's crust and mantle. Due to the near‐vertical incidence of the XKS arrivals, the resulting splitting parameters (fast polarization orientations and splitting times) have an excellent horizontal but poor vertical resolution, resulting in considerable ambiguities in the geodynamic interpretation of the measurements. Here we use P‐to‐S converted phases from the Moho and the 410‐ (d410) and 660‐km (d660) discontinuities to investigate anisotropy layering beneath Southern California. Similarities between the resulting splitting parameters from the XKS and P‐to‐S converted phases from the d660 suggest that the lower mantle beneath the study area is azimuthally isotropic. Similarly, significant azimuthal anisotropy is not present in the mantle transition zone on the basis of the consistency between the splitting parameters obtained using P‐to‐S converted phases from the d410 and d660. Crustal anisotropy measurements exhibit a mean splitting time of 0.2 ± 0.1 s and mostly NW‐SE fast orientations, which are significantly different from the dominantly E‐W fast orientations revealed using XKS and P‐to‐S conversions from the d410 and d660. Anisotropy measurements using shear waves with different depths of origin suggest that the Earth's upper mantle is the major anisotropic layer beneath Southern California. Additionally, this study demonstrates the effectiveness of applying a set of azimuthal anisotropy analysis techniques to reduce ambiguities in the depth of the source of the observed anisotropy.

Seismic Anisotropy and Mantle Flow in the Sumatra Subduction Zone Constrained by Shear Wave Splitting and Receiver Function Analyses

“…Before the computation of the RFs, all the seismograms were band‐pass filtered in the frequency band of 0.08 to 0.8 Hz. To improve the accuracy of the picked arrival times of the Pms phase on the RFs, all the RFs were corrected for epicentral distance (Kong et al, ). The strength and fast orientation of crustal anisotropy at a given station were obtained by fitting the Pms arrivals using a sinusoidal function.…”

Adjoint‐State Traveltime Tomography for Azimuthally Anisotropic Media and Insight Into the Crustal Structure of Central California Near Parkfield

“…Although the technique is simple in theory, computationally inexpensive and possesses a good resolving ability in lateral directions, shear wave splitting has poor resolution in the vertical direction, especially when seismic anisotropy is resolved by core phases such as SKS and SKKS (Fouch & Rondenay, 2006; Long, 2013). Anisotropic receiver function analysis usually extracts seismic anisotropy information from teleseismic P‐to‐ S conversions (e.g., Bar et al., 2019; Kong et al., 2018). It has extensive depth resolution at the wavelength scale of the P‐to‐ S phase (Fouch & Rondenay, 2006), which is much higher than that of the shear wave splitting.…”

Localized Anisotropy in the Mantle Transition Zone Due to Flow Through Slab Gaps

“…Since small delay times often yield undetectable Ps signal on the SH component (Montagner et al., 2000), stacking many waveforms is often required and attempts to use the two phases are limited to areas with strong anisotropy (Kong et al., 2018; Vinnik & Montagner, 1996). Based on their piercing points at 500 km depth, we stacked the receiver functions that sample the transition zone in 200 km radius caps.…”