Isolating retrograde and prograde Rayleigh-wave modes using a polarity mute

Abstract

Estimates of S-wave velocity with depth from Rayleighwave dispersion data are limited by the accuracy of fundamental and/or higher mode signal identification. In many scenarios, the fundamental mode propagates in retrograde motion, whereas higher modes propagate in prograde motion. This difference in particle motion (or polarity) can be used by joint analysis of vertical and horizontal inline recordings. We have developed a novel method that isolates modes by separating prograde and retrograde motions; we call this a polarity mute. Applying this polarity mute prior to traditional multichannel analysis of surface wave (MASW) analysis improves phase velocity estimation for fundamental and higher mode dispersion. This approach, in turn, should lead to improvement of S-wave velocity estimates with depth. With two simple models and a field example, we have highlighted the complexity of the Rayleigh-wave particle motions and determined improved MASW dispersion images using the polarity mute. Our results show that we can separate prograde and retrograde signals to independently process fundamental and higher mode signals, in turn allowing us to identify lower frequency dispersion when compared with single component data. These examples demonstrate that the polarity mute approach can improve estimates of S-wave velocities with depth.

Improved Holistic Analysis of Rayleigh Waves for Single- and Multi-Offset Data: Joint Inversion of Rayleigh-Wave Particle Motion and Vertical- and Radial-Component Velocity Spectra

“…175, (2018) Improved Holistic Analysis of Rayleigh Waves for Single-and Multi-Offset Data: JointUnlike the polarity analysis proposed by Gribler et al (2016) and the RVSR curve used in Dal Moro et al (2015aMoro et al ( , b, 2016, the RPM frequency-offset data can be determined even when using vertical and horizontal geophones with different response curves.…”

“…The first point is quite simple and does not require much explanation; the average polarity considered by Gribler et al (2016) is necessarily a rough value with a relatively limited meaning because the actual Rayleigh-wave motion is a function of the frequency (and offset). On the other side, because of its practical consequences, it is probably useful to clearly illustrate the second property of the RPM frequency curve.…”

“…In this respect, compared to the polarity analysis presented in Gribler et al (2016), the RPM frequency curve benefits in particular from two important features:…”

“…On the other hand, the method presented in Gribler et al (2016) is based on the analysis of the amplitudes; therefore; it requires analyzing data acquired through vertical and horizontal geophones with the same response curve.…”

Estimation of porosity and water saturation in dual-porosity pyroclastic deposits from joint analysis of compression, shear, and electromagnetic velocities

“…We performed MASW by modifying the approach of Gribler et al (2016), which requires Rayleigh waves across off-end shot gathers. Offsets nearer than approximately 20 m often contain high-amplitude body waves that degrade the dispersion curve clarity.…”