Unique Algorithm Which Takes Into Account Source Wave Travel Paths When Estimating Absorption Values from DST Data Sets-Paper

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The paper presents a new method for estimating soil absorption and damping from downhole seismic testing (DST), which supports dynamic soil-response analysis. Conventional spectral ratio techniques can produce unreliable results in near-surface DST because they assume seismic waves follow the same path at different depths, whereas actual raypaths vary. The method is also sensitive to measurement noise and waveform distortion.<br /><br />The proposed Forward Modeling Downhill Simplex Method Absorption Analysis (FMDSMAA) works in the time domain. It uses measured waveform amplitudes and estimated in-situ properties—including interval velocities, raypaths, incidence and reflection angles, and soil density—to model amplitude changes with depth. The algorithm estimates absorption values for as many as eight layers, together with a geometric-spreading exponent, by minimizing differences between measured and modeled amplitude ratios. It also reports a residual error estimate and allows users to set limits on plausible quality-factor values. Consistent seismic-source energy across the profile is required.<br /><br />A simulated 12-layer test showed close agreement between assumed and recovered absorption, quality-factor, and damping values, supporting the method’s performance under the tested conditions. The authors conclude that FMDSMAA addresses key limitations of spectral ratio analysis, but note that validation with field data and direct comparison with the conventional technique remain future work.

Keywords

soil absorption

damping

downhole seismic testing

forward modeling

time-domain analysis

spectral ratio technique

quality factor

geometric spreading

waveform amplitudes

soil-response analysis