Array observations of the shear-coupled PL wave

Observations from the NARS array in western Europe of a shallow earthquake in northwest Africa are used to study shear-coupled PL-wave (SPL) excitation near the source and receiver. Numerical experiments suggest that average crustal thickness and velocity are important in defining the frequency content of SPL. If crustal structures in the source and receiver areas are similar and the upper mantle velocity gradients are positive, then large SPL waves can be generated. Using the near-receiver velocity structure that was determined from previous NARS studies, we model the near-source structure for an earthquake in northwest Africa. Although the model is subject to significant trade-offs in layer thicknesses and velocities in the near-source structure, SPL waveforms could be a useful auxiliary data set to other seismological structure studies.