Automated Waveform Assembling for Full-3D Tomography

Alan Juarez, & Thomas Jordan

Submitted August 11, 2017, SCEC Contribution #7504, 2017 SCEC Annual Meeting Poster #025

Seismological research has broadly focused on developing techniques for extracting information from seismograms and constructing models of seismic source excitation and Earth structure. Examples of modeling methods include the measurement and inversion of travel times, phase and group velocities, and amplitude decay. However, these classical techniques are limited by the ability to identify specific seismic phases. For seismograms computed for 1D Earth models, the synthesis of standard seismic phases is relatively straightforward (e.g., through the numerical calculation of discrete traveling modes or generalized rays), but these conventional methods are of limited utility for seismic waves propagating through structures with strong 3D heterogeneity. We present a new technique for systematically separating seismic phases using time-frequency spectra computed by the S-transform (Stockwell et al., 1996), which is a linear transformation based on Gaussian wavelets. Iterative waveform stripping decomposes seismograms into a finite set of waveforms, and the tomographic Fréchet kernels for each waveform are calculated. Subsets of waveforms are then combined into well-organized seismic phases through an assembling procedure that optimizes the localization of the waveform in the time domain and the Fréchet kernel in the spatial domain. Weights for the combinations are estimated by the Sum-of-Wavelets Theorem (Gee & Jordan, 1992). This algorithm allows the identification of seismic phases that are not predicted by a 1D structural model, such as basin-edge conversions, increasing the structural information that can be derived from a single seismogram. We show examples of seismogram decomposition and tomographic kernels computed using synthetic and real data from earthquakes in Southern California.

Key Words
Waveform Analysis, Fréchet Kernel, S-Transform, Seismic Tomography

Citation
Juarez, A., & Jordan, T. (2017, 08). Automated Waveform Assembling for Full-3D Tomography. Poster Presentation at 2017 SCEC Annual Meeting.


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