Wiggle Trace: Seismic Amplitude Display, Variable Area Shading, and Reflection Interpretation

A wiggle trace is the classic way of displaying a single seismic trace as an oscillating line that swings left and right of a vertical zero, or null, axis, where the horizontal deflection at any point represents the recorded reflection amplitude and the direction of deflection represents polarity. Each trace is the time series of ground motion or pressure recorded at one receiver location after a seismic source fires, and a seismic section is built by plotting many such traces side by side, with two-way travel time increasing downward and surface position running across the display. On a wiggle trace a strong reflector produces a large excursion, a weak reflector a small one, and a reversal in the sign of the reflection coefficient flips the wiggle to the opposite side of the null line, which is how an interpreter reads bright spots, tuning effects, and polarity reversals that may indicate fluid or lithology changes. In practice the pure wiggle is usually combined with variable-area shading, in which the peaks on one side of the null axis are filled solid, most often in black, so that continuous reflectors appear as bold shaded bands that the eye can track laterally across faults and folds. This variable-area-wiggle presentation is the traditional workhorse of seismic processing quality control because it shows both the exact waveform and an easily followed reflector geometry, whereas variable-density and full-colour displays, which map amplitude to a colour scale, are generally preferred for detailed seismic interpretation and amplitude analysis. The wiggle trace sits at the output end of a long processing chain that includes deconvolution, static and normal-moveout corrections, stacking, and migration, and the fidelity of its wiggles depends on how well amplitude has been preserved through that chain. In the Western Canadian Sedimentary Basin, interpreters use wiggle and variable-area displays to map Cardium, Viking, and Mannville reflectors, to pick the top of carbonate reefs such as Leduc and Nisku, and to tie synthetic seismograms generated from well logs to the field data. Displays are annotated in both time (milliseconds) and, after depth conversion, in m alongside ft, and the interpreted horizons feed prospect maps, well planning, and reserve estimates disclosed under National Instrument 51-101 and reviewed against AER well and geological data.

Reading Polarity and Tuning on Wiggle Displays

Because a wiggle trace preserves the full waveform, it is the display where interpreters judge polarity conventions and tuning effects most directly. Under a standard polarity convention, an increase in acoustic impedance produces a defined peak or trough, and a flip to the opposite deflection signals a decrease, such as gas-charged sand beneath a shale. Where two reflectors are closer than a quarter wavelength, their wiggles interfere and tune, boosting or cancelling amplitude, which the interpreter must recognize before reading amplitude as a direct fluid indicator. Seeing the actual wiggle shape, rather than a smoothed colour band, is what makes these subtle waveform effects visible during quality control and detailed analysis.

From Wiggle Trace to Mapped Horizon

Interpretation on a wiggle or variable-area section proceeds by picking a consistent phase, a peak or a trough, along a target reflector across every trace, then carrying that pick through the seismic volume to build a time-structure map. In the WCSB this is how the top of a Leduc reef or the base of the Cardium is traced across a survey. The picks are tied to wells through synthetic seismograms, converted from time to depth in m alongside ft using a velocity model, and posted as structure and amplitude maps that guide horizontal well placement and delineation drilling, with the underlying wiggle character always available for re-inspection where a pick is ambiguous.

Related Terms

A wiggle trace is the display form of the output of a seismic survey, the acquisition program that records the reflections in the first place. Reading it is the entry point to seismic interpretation, where reflectors become mapped geologic horizons. Its fidelity depends on migration and other processing that repositions energy to its true subsurface location, and it is anchored to geology through a synthetic seismogram built from well logs to tie tops to reflections.

Real-World WCSB Scenario: Tying a Synthetic to Field Data at a Cardium Prospect

A geophysicist evaluating a Cardium horizontal prospect near Pembina in central Alberta acquired a 3D survey and needed to confirm which wiggle reflector corresponded to the Cardium sand before committing a CAD 6 million horizontal well. Using sonic and density logs from an offset vertical well, the team built a synthetic seismogram displayed as a wiggle trace and overlaid it on the field variable-area section. The synthetic's peak-trough pattern matched a specific reflector once a small static shift was applied, confirming the Cardium pick and revealing a subtle polarity character consistent with the productive sand.

With the reflector confirmed, the interpreter mapped the Cardium time-structure across the survey, converted it to depth, and steered the horizontal landing point to the structurally optimal position. The well came in on prognosis within a few metres, and the confident wiggle-based tie was credited with avoiding a mislanded lateral that would have cost hundreds of thousands of dollars to correct.