Seismic geomorphology: reading paleo-landscapes from 3D volumes

The seismic geomorphology workflow

• Regional horizon mapping. Identify a regional marker — typically a sequence boundary (§4.2), MFS, or major flooding surface — and pick it throughout the 3D volume.
• Horizon flattening (optional). Transform the volume so the horizon is flat, removing structural deformation. What remains is the paleo-relief of the depositional surface — the ancient landscape geometry.
• Amplitude extraction / attribute slice. Extract values of a seismic attribute (RMS amplitude, coherence, spectral decomposition) AT the horizon or within a time window above/below it. The result is a 2D map where each pixel value corresponds to a physical property of the rock at that location.
• Paleo-landscape interpretation. Read the map as a landscape. Sinuous bright trails are channels. Lobate patterns are fans. Linear arcuate features are shorelines. Circular bright spots are reefs or distributary-mouth bars. Annotate features, classify each as a depositional-system type from §4.3–§4.5.
• Build depositional model. Combine the amplitude map with well data, biostratigraphy, and rock-physics analysis to predict reservoir distribution, quality, and volume.
• Iterate and refine. Pick additional horizons through the section to see how the landscape EVOLVED over time. Multiple time-slice maps together tell the story of a basin’s depositional history.

Exercise — read the paleo-landscape

• The widget opens in Overview. You are seeing a complete paleo-landscape map. On the left: coastal plain with meandering rivers. In the middle: shoreline with a prograding delta. On the right: shelf break, slope with a sinuous submarine channel, and a basin-floor fan.
• Switch to Fluvial domain. The coastal plain lights up; the trunk river and tributary stand out. Notice the sinuous channels and the small abandoned oxbow lakes. This is the source of sediment for everything downstream.
• Switch to Coastal domain. The shoreline, delta lobe, and distributary channels become the focus. This is where river sediment first encounters marine water and deposits as delta-front and shoreface sands — classic reservoir targets.
• Switch to Deep-water domain. The slope channel and basin-floor fan light up. Sediment from the river has traveled all the way across the landscape, down the slope, and built a prograding fan. This is where the prize targets live.
• Switch to Workflow. Overlay markers show the three-step seismic-geomorphology process — pick a horizon, extract amplitude on it, interpret the resulting paleo-landscape.
• Return to Overview. Now you see the whole landscape as an integrated scene. A modern interpreter’s mental model of a basin IS this kind of composite map: rivers feeding deltas feeding slopes feeding fans, all in one geographic whole.

Why the map view revolutionized interpretation

Before the 3D-seismic era, interpreters worked mostly in cross-section and built mental maps piece by piece. Finding a channel required crossing it on a seismic line and then guessing its planform from sparse line-to-line correlation. Modern 3D + horizon amplitude extraction gives the planform DIRECTLY — every feature visible as its actual geographic shape.

Specific consequences:

• Speed. A single horizon amplitude extraction reveals channels across hundreds of km² in a few minutes of processing time.
• Accuracy. Planform geometry is no longer inferred — it is measured. Channel width, length, sinuosity, and bifurcation pattern can be quantified directly.
• New discoveries. Entire classes of exploration targets became visible for the first time — distal thin-bedded turbidites, small stratigraphic pinchouts, subtle channel-margin traps.
• Integration with geology. Maps are the universal language of geology — sharing interpretations with geologists, engineers, and executives is now natural because everyone sees the same kind of map.
• Drill-decision support. Pre-drill prediction of reservoir geometry is now quantitative, not qualitative, because the paleo-landscape is mapped in advance.

Integration with Part 3 (structural) and Parts 5-6 (rock physics + attributes)

Seismic geomorphology doesn’t replace structural interpretation — it complements it. A modern interpretation workflow combines:

• Structural framework (Part 3). Build the 3D structural model from horizon + fault picking. This gives the TRAP geometry.
• Stratigraphic framework (Part 4). Use sequence stratigraphy (§4.2) to subdivide the section into sequences. Use seismic geomorphology (§4.6) to map depositional systems on key horizons.
• Rock-physics analysis (Part 5). Use AVO and inversion to distinguish sand from shale and predict fluids within the mapped depositional systems.
• Attribute analysis (Part 6). Refine geomorphology interpretation using coherence, spectral decomposition, and RGB-blended attributes to enhance feature recognition.

The integrated product is a reservoir model: trap geometry (structural), reservoir geometry + quality (stratigraphic + geomorphic), and fluid prediction (rock-physics + attributes), all on the same 3D volume. This is what modern exploration delivers, and it is the framework within which every major discovery of the 2000s-2020s has been made.

Practical tips for reading a horizon amplitude map

• Start with the bright features. Bright spots typically indicate sand or hydrocarbon; darker areas are typically shale or non-reservoir. Bright spots deserve your attention first.
• Trace sinuous features. Curvilinear bright trails are almost always CHANNELS — classify by sinuosity (§4.4) and setting.
• Look for lobate or radial patterns. These are deltas, fans, or channel-mouth bars. Identify the feeder (upstream) and the distal end (downstream).
• Identify linear boundaries. Straight or gently curved lines often mark paleo-shorelines, shelf breaks, or fault-controlled depositional edges.
• Note scale. A feature 50 m across is a sub-seismic curiosity; 500 m is a reservoir target; 5 km is a play. Scale tells you significance.
• Check context. A sinuous feature on a slope is a submarine channel; the same geometry on a coastal plain is a fluvial channel. Interpret geometry in context.
• Use multiple attributes. RMS amplitude, coherence, spectral decomposition each reveal different aspects of the landscape. Combining them (e.g., RGB blending, see §6.5) often reveals features invisible on any one attribute alone.

Pitfalls and limits

• Resolution limits. Features smaller than ~¼-wavelength seismic resolution (often 8–40 m vertically, 25–100 m laterally) are not resolvable. A 30-m-wide channel cannot be mapped with conventional seismic.
• Amplitude ≠ geology. Amplitude is a proxy for rock properties, but hydrocarbon effects, tuning, and processing artifacts can produce amplitude anomalies that don’t correspond to depositional features. Always cross-check with section view and rock-physics.
• Noise. Migration artifacts, acquisition footprint, and multiples can create false geomorphic features. Verify that features are consistent across multiple attribute types and multiple horizons.
• Oversimplification. The schematic paleo-landscape we show is clean; real horizon extractions have more noise, more complexity, more ambiguity. Calibration against well data is essential.
• Present-day context bias. It’s tempting to look at a horizon-slice and imagine the modern coastline. Remember — this is a PALEO-landscape. The orientation, setting, and climate of the paleo-world may have been radically different.