The structure of continental crust: comparison of body wave apparent incidence angle and receiver function results

Abstract:

The dense coverage of the EarthScope USArray presents an unprecedented opportunity to systematically investigate the structure of the continental crust across different tectonic regimes. Receiver function analysis of body wave arrivals can isolate converted phases (Ps or Sp) produced across velocity discontinuities beneath a seismometer and constrain relative vertical density and seismic velocity variations. Analysis of receiver functions computed for stations across the footprint of the USArray can be used to constrain both the strength and topography of crustal interfaces. However, complications in receiver function analysis arise from trade-offs among compressional (Vp) and shear (Vs) wave velocity variations, as well as reverberations caused by sediment-dominated regions within the United States.

We show that by measuring the apparent incidence angle of P waves – their relative amplitude on the vertical and radial components of the seismogram – computed for different time-windows, we can obtain an estimate of crustal Vs layering at each station. The calculated Vs estimate is in terms of absolute as opposed to relative velocity variations and is independent of Vp. Using synthetic waveforms, we quantify to what extent absolute velocity inferences obtained using the apparent-incidence angle method are affected by multiple reverberations in shallow layers. We then use both synthetics and data to evaluate the potential of the apparent incidence method for constraining anisotropy, and compare it to receiver functions. Finally, we compare and contrast results from receiver function and apparent incidence angle analyses in different tectonic settings across North America.