The Use of Seismic Trace Characterization to Guide the Analysis of DST Results to Obtain More Accurate Soil Parameters-Paper

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The paper presents Seismic Trace Characterization (STC), a method for assessing downhole seismic testing (DST) data quality and guiding analysis to produce more reliable shear-wave interval velocities. Accurate near-surface shear-wave velocities are important for evaluating earthquake-related liquefaction potential, but near-surface traces are often affected by noise, reflections, and other distortions.

STC evaluates five trace metrics: <strong>linearity (LIN)</strong>, indicating directional consistency across sensor axes; <strong>cross-correlation coefficient (CCC)</strong>, measuring similarity between traces; <strong>signal shape parameter (SSP)</strong>, assessing how closely the frequency spectrum resembles an ideal bell-shaped curve; <strong>peak symmetry differential (PSD)</strong>, identifying skewed or distorted waveform peaks; and <strong>signal-to-noise ratio (SNR)</strong>, estimating the contribution of desired signal frequencies.

The metrics serve different purposes. LIN helps determine whether to analyze the combined waveform or use a preferred sensor axis. CCC, SSP, and PSD help identify trace-quality problems and select processing techniques. The paper demonstrates strategies including batch signal decay for ringing, signal feature decay to isolate less-distorted waveform features, and aggressive low-pass filtering followed by signal feature decay when multiple quality metrics are poor. SNR can help compare results from opposite source directions when calculated velocities differ substantially.

Examples using real data illustrate how STC can guide processing decisions and flag less reliable velocity estimates. The authors conclude that the five metrics provide a practical framework for assessing DST trace quality and improving interval-velocity analysis, particularly in the challenging near-surface zone.

Keywords

seismic trace characterization

downhole seismic testing

shear-wave interval velocity

near-surface velocity

trace quality assessment

signal-to-noise ratio

cross-correlation coefficient

linearity metric

peak symmetry differential

low-pass filtering