Strong SH‐to‐Love Wave Scattering off the Southern California Continental Borderland

Abstract

Seismic scattering is commonly observed and results from wave propagation in heterogeneous medium. Yet deterministic characterization of scatterers associated with lateral heterogeneities remains challenging. In this study, we analyze broadband waveforms recorded by the Southern California Seismic Network and observe strongly scattered Love waves following the arrival of teleseismic SH wave. These scattered Love waves travel approximately in the same (azimuthal) direction as the incident SH wave at a dominant period of ~10 s but at an apparent velocity of ~3.6 km/s as compared to the ~11 km/s for the SH wave. Back projection suggests that this strong scattering is associated with pronounced bathymetric relief in the Southern California Continental Borderland, in particular the Patton Escarpment. Finite‐difference simulations using a simplified 2‐D bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers. The modeling suggests a relatively low shear wave velocity in the Continental Borderland.

S‐to‐Rayleigh Wave Scattering From the Continental Margin Observed at USArray

“…Body-to-surface wave scattering due to surface topography has been studied since the 1960s (Levander, 1990). Converted surface waves similar to our USArray observations have been observed from scattered P waves at the Japan Trench (Maeda et al, 2014), at the Pacific Trench of Mexico (Dominguez et al, 2011), for deep events near Australia (Furumura et al, 1998), and most recently by Yu et al (2017) who reported SH-to Love wave scattering off the Southern California Continental Borderland for deep events in the Fiji region. It is important to be aware of these large-amplitude arrivals cutting across body wave phases, as they could interfere with analyses of direct or converted phases in this part of the wavefield, causing problems for migration, back projection, or attenuation tomography.…”

Imaging Strong Lateral Heterogeneities Across the Contiguous US Using Body‐To‐Surface Wave Scattering

“…Figures 10a and 10b). The result is consistent with previous findings in this region (Buehler et al, 2018;Yu et al, 2017a). However, there is no detection of strong scatterers along the continental slope of Atlantic Plains, where topographic gradients are also significant.…”

“…Body-to-surface wave scattering, including both P/SV-to-Rayleigh wave scattering and SH-to-Love wave scattering, has been observed in many locations around the world (e.g. Bannister et al, 1990;Buehler et al, 2018;Furumura et al, 1998;Maeda et al, 2014;Yu et al, 2017a).…”

“…Moreover, if the delay time with respect to some reference phases can be measured, it is then possible to use the scattered surface waves to locate strong lateral heterogeneities. For example, Yu et al (2017a) The contiguous US is rich in structural heterogeneities both at the surface and in the underlying lithosphere. To first order, the contiguous US can be roughly divided into the western, central and eastern US ( Figure 1).…”

Imaging Upper‐Mantle Structure Under USArray Using Long‐Period Reflection Seismology

“…Finally, there is the possibility that this dipping feature is some kind of artifact related to scattering of incoming S waves off the western continental margin, such as the surface-wave scattering observed by Yu et al (2017) and Buehler et al (2018), that is, a feature analogous to a diffraction hyperbola in reflection seismology. To test this idea, we generated a synthetic data set in which we replaced each of our observed seismograms with simple Ricker pulses at offset times from direct S that were derived from the sum of the predicted iasp91 source-to-scatterer time and a scatterer-to-receiver time computed from an assumed surface-wave velocity.…”