downdip

Downdip is a geological term used to describe the direction along which a rock bed, fault plane, fracture set, or other planar feature steepens or deepens as it dips away from the exposed edge into subsurface strata. The concept derives from dip, the angle between the plane and the horizontal, and the downdip direction is the sense along the dip toward greater burial depth. In practice, downdip is determined by the compass azimuth of the dip direction.

In sedimentary geology, downdip indicates the direction toward deeper strata or thicker sections; in a cross-section, it is the direction of increasing burial depth along bedding planes. In structural geology, the concept applies to faults and fractures: downdip directions indicate the downdip side of a fault or faulted zone.

Examples: If a bed dips 15 degrees to the south, the downdip direction is toward the south. In a map of a gently dipping sequence, the downdip edge may define progressively deeper units away from the near-surface exposure. In petroleum geology and hydrogeology, downdip orientation helps in predicting fluid flow, reservoir geometry, and drainage patterns, especially where inclined beds or fault blocks influence connectivity.

Difference with updip: updip is toward the uphill or shallower edge, opposite the downdip direction.

Limitations: In complex structures with multiple folds, tilting, or varying dip directions, identifying a single downdip direction can be ambiguous and may require local measurements and context.