Yale University
New Haven
Email:
jeffrey.park@yale.edu
poster/oral: oral
| Teleseismic P-waves are followed by a series of scattered waves, particularly P-to-S converted phases, that form a coda. The sequence of scattered waves on the horizontal components can be represented by the receiver function (RF) for the station, and may vary with the approach angle and azimuth of the incoming P wave. We have developed a frequency-domain RF estimator using multiple-taper correlation (MTC) estimates, using the pre-event noise spectrum for frequency-dependent damping. The multi-taper spectrum estimates are leakage resistant, so low-amplitude portions of the P-wave spectrum can contribute usefully to the RF estimate. The coherence between vertical and horizontal components can be used to obtain a frequency-dependent uncertainty for the RF. We compare the MTC method with two popular methods for RF-estimation, time-domain deconvolution (TDD) and spectral division (SPD), both with damping to avoid numerical instabilities. Multiple-taper correlation RFs are more resistant to signal-generated noise in test cases, though a ``coherent'' scattering effect, like a strong near-surface organ-pipe resonance in soft sediments, will overprint the Ps conversions from deeper interfaces. In favorable signal-to-noise conditions, MTC RF estimates retrieve shallow (< 100 km) P-to-S conversions at frequencies approaching 5 Hz. In order to see deeper in the mantle, we modify the multiple-taper parameters (adjusting its frequency bandwidth for spectral smoothing) to estimate spectral correlation across either (1) a cluster of seismic events, or (2) a cluster of neighboring seismic stations. This allows the retrieval of Ps converted-phases at longer time delay, increasing sensitivity of multiple-taper RFs to mantle features at greater depth. A second modification is a migration scheme in the frequency domain that preserves the uncertainty estimates of the spectral correlation estimator, so that migration can downweight poorly resolved RFs while following the moveout of the Ps delays with epicentral distance. |