A comparison of phase inversion and traveltime tomography for processing near-surface refraction traveltimes

Abstract

With phase inversion, one can estimate subsurface velocities using the phases of first-arriving waves, which are the frequency-domain equivalents of the traveltimes. Phase inversion is modified to make it suitable for processing traveltimes from near-surface refraction surveys. The modifications include parameterizing the model, correcting the observed phases, and selecting the complex frequency. This modified phase inversion is compared to traveltime tomography. For two comparisons using computer-simulated traveltimes, the difference between the estimated and correct models, the residual mean, and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography. For a comparison using field data from an S-wave refraction survey, both methods estimate models that are consistent with the known geology. Nonetheless, the phase-inversion model includes small-scale features in the bedrock that are geologically plausible; the residual mean and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography.

Computer programs for forward and inverse modeling of acoustic and electromagnetic data

“…In all cases, the estimated model was close to the correct model, when the spatial resolution of the inversion was accounted for. Additional information about these tests is published in Ellefsen (2009) and Burton and Ellefsen (2011). Another set of tests involved field data.…”

“…Traveltimes were processed with phase inversion (using program WaveformInv) and with traditional traveltime tomography; both processing methods used the same starting model. The estimated models and the residuals for both processing methods were compared, and the results are published in Ellefsen (2009). For this test, the files used for the phase inversion are in subdirectory Examples\PhaseIn-vRefractionTimes.…”

“…The mathematical theory related to forward and inverse modeling of electromagnetic data is described in Ellefsen and others (2007), Ellefsen and others (2009), and Ellefsen andothers (2010 and. Consequently, these theories are not repeated here.…”

“…The mathematical theory related to forward and inverse modeling of acoustic data is described in Ellefsen (2009). The mathematical theory related to forward and inverse modeling of electromagnetic data is described in Ellefsen and others (2007), Ellefsen and others (2009), and Ellefsen andothers (2010 and.…”

Blind Test of Methods for Obtaining 2-D Near-Surface Seismic Velocity Models from First-Arrival Traveltimes

“…There are many different methods for obtaining a velocity model from seismic refraction first-arrival times, ranging from forward modeling to analytic and geometrical methods to inverse and tomographic methods (e.g., Palmer, 1980;Zelt and Smith, 1992;Sheehan et al, 2005;Ellefsen 2009). Near-surface P-and S-wave velocity models provide essential constraints in applications ranging from hydrologic characterization to site hazard evaluation (e.g., Deen and Gohl, 2002;Asten et al, 2005;Zelt et al, 2006;Powers et al, 2007;Martí et al, 2008;Yordkayhun et al, 2009), but often these models include little or no quantitative estimation of uncertainty, resolution or non-uniqueness.…”