Automatic Shear Wave Splitting Measurements at Mt. Ruapehu Volcano, New Zealand

Abstract

<p>This thesis presents an automatic shear wave splitting measurement tool and the results from its application to data recorded in the vicinity of Mt. Ruapehu volcano on the North Island of New Zealand. The best methodology and parameters for routine automatic monitoring are determined and approximately 10,000 events are processed. About 50% of all S-phases lead to measurements of acceptable quality. Results obtained with this technique are reproducible and objective, but more scattered than results from manual measurements. The newly developed automatic measurement tool is used to measure shear wave splitting for previously analysed data and for new data recorded in 2003-2007. In contrast to previous studies at Mt. Ruapehu, we have a larger and continuous data set from numerous three-component seismic stations. No major temporal changes are found within the new data, but results vary for di erent station locations. I</p>

Mantle Flow Induced by the Interplay of Downgoing Slabs Revealed by Seismic Anisotropy Beneath the Sula Block in Eastern Indonesia

“…As shear wave splitting has grown in popularity as a tool for measuring seismic anisotropy, different packages for splitting analysis have been developed. In this study, we used the multiple frequency automatic splitting technique software package (MFAST; Savage et al., 2010; Teanby et al., 2004; Wessel, 2010) on the local and teleseismic S waves to determine φ and δt. MFAST builds upon the eigenvalue method (Silver & Chan, 1991) and conducts an automatic grid search for a best‐fitting solution by incremental shifting the analysis window within a specified waveform segment.…”

“…We carefully inspected all waveforms manually, and only used the data with SNR greater than 3. We then used the MFAST program (Savage et al., 2010; Teanby et al., 2004; Wessel, 2010) to constrain the anisotropic seismic parameters φ and δt. Following the procedures described in Teanby et al.…”

“…We carefully inspected all waveforms manually, and only used the data with SNR greater than 3. We then used the MFAST program (Savage et al, 2010;Teanby et al, 2004;Wessel, 2010) to constrain the anisotropic seismic parameters φ and δt. Following the procedures described in Teanby et al (2004) and Wüstefeld et al (2008), only those results which match the following criteria are retained: (a) minimal energy on the transverse component of SK(K)S waves or on the perpendicular component of incoming polarization direction for local/teleseismic S waves; (b) good correlation between the fast and slow waveforms; (c) linear particle motion; (d) a unique, well-defined error surface.…”

Testing the Validity of Shear-Wave Splitting Measurements in the Presence of Scattering Using Synthetic Waveform Modelling

“…To obtain measurements of the SWS in our synthetic waveforms, we used the Multiple Filter Automatic Splitting Technique (MFAST) (Savage et al, 2010;Teanby et al, 2004;Wessel, 2010). The core technique MFAST uses to generate measurements is a grid search over possible values of fast polarisation (φ) and delay time (δt) with an inverse splitting operator derived from Silver and Chan (1991), to find the splitting operator and parameters that maximises the linearity of the particle motion.…”