Constraining sedimentary basins in the Southeastern US using P-to-s receiver functions

The depth, seismic velocity, and geometry of basins play a fundamental role in dictating the amplitude and duration of ground shaking during an earthquake, (e.g. Johnson and Silva 1981, Olsen,2000; Field and Peterson, 2000), which correlate significantly with earthquake damage. P-to-s receiver functions (RFs) are sensitive to sharp changes in impedance contrasts such as at the base of a basin. The impedance contrast between a basin and underlying basement rock is often so large that S-wave basin reverberations overprint deeper seismic signals, rendering interpretation of crustal thickness difficult. Here, we present a method that 1) characterizes useful basin properties for seismic hazard assessment, and 2) removes basin contamination from P-to-s RFs to obtain more accurate crustal thickness estimates.

Due to the impedance contrast between the basin and basement rock, P-to-s RFs are particularly sensitive to S-wave reverberations in the basin. Computing the autocorrelation of the RF allows us to measure the S-wave reverberation time (T_ss). This time is directly related to the basin resonant frequency, allowing for estimates at broadband stations across the southeastern US. We validate against resonant frequencies estimated using the spectral ratio method applied to RFs. The spectral ratio method quantifies amplification due to the sedimentary basin across a range of frequencies. In addition, we use high frequency (4Hz) P-to-s RFs to determine the relative arrival time of the direct basin P-to-s conversion (T_S-P). While these two measurements (T_SS and T_S-P) alone cannot uniquely determine V_P, V_S, and thickness of the basin rocks, we incorporate the mud line equation describing the relationship between V_P and V_S for unconsolidated sediments (Brocher et al. 2005), to calculate these basin properties beneath each seismic station. In addition to constraining important basin properties, we demonstrate that the measurements of T_SS and T_S-P and the application of a resonance removal filter (Yu et al. 2015) to P-to-s RFs are necessary to reliably constrain crustal thickness and V_P/V_S beneath seismic stations on sedimentary basins. We assess the performance of our approach to constraining sedimentary structure by comparing our results to previous studies across the southeastern US.