Noise reduction and detection of weak, coherent signals through phase-weighted stacks

Abstract

We present a new tool for efficient incoherent noise reduction for array data employing complex trace analysis. An amplitude-unbiased coherency measure is designed based on the instantaneous phase, which is used to weight the samples of an ordinary, linear stack. The result is called the phase-weighted stack (PWS) and is cleaned from incoherent noise. PWS thus permits detection of weak but coherent arrivals. The method presented can easily be extended to phase-weighted cross-correlations or be applied in the z-p domain. We illustrate and discuss the advantages and disadvantages of PWS in comparison with other coherency measures and present examples. We further show that our non-linear stacking technique enables us to detect a weak lowermantle P -t o 4 conversion from a depth of approximately 840 km on array data. Hints of an 840 km discontinuity have been reported; however, such a discontinuity is not yet established due to the lack of further evidence.

Model P Wave Multipathing at Regional Distances in Southeast Asia

“…In this study we commonly use 3-pole Butterworth bandpass filters, and phase-stack weighted (PSW) beams. The PSW beams amplify coherent energy but induce less waveform distortion than n th root beams (Schimmel & Paulssen, 1997). We find that this leads to more precise slowness estimates.…”

“…Movies that show power as a function of ray parameter, backazimuth, and time can also be output. Our measure of coherence is the stack of the instantaneous phases of the aligned traces, which varies from 1 for perfect coherence to 0 for perfect incoherence (Schimmel & Paulssen, 1997). In this work, the data are generally filtered around 1.0 Hz, and we have found a window length of 2 s provides good results.…”

Broadband waveform modeling with the spectral element method on Earth Simulator for the study of the structure at the top of the Earth's outer core

“…After adjusting the arrival times of S2KS phases using the cross-correlation method and normalizing the amplitude with its maximum for each trace, the phaseweighted stack (Schimmel and Paulssen, 1997) Furthermore, additional runs are conducted by incorporating 3D mantle models. The first model is S20RTS (Ritsema et al, 1999), which is originally involved in the mesh generator of the SEM.…”

Constraints on rigid zones and other distinct layers at the top of the outer core using CMB underside reflected PKKP waves

“…Two different stacking methods, the N th-root stacking (Muirhead, 1968;Kanasewich, 1973) and the phaseweighted stacking (Schimmel and Paulssen, 1997), are employed. Both methods are designed to be more effective in enhancing coherent signals than the regular linear stacking method.…”