Anticlinal

An anticline is an arch-shaped fold in rock in which rock layers are upwardly convex.
A typical anticline is convex up in which the hinge or crest is the location where the curvature is greatest, and the limbs are the sides of the fold that dip away from the hinge.
The oldest rock layers form the core of the fold, and outward from the core progressively younger rocks occur.
Anticlines can be recognized and differentiated from antiforms by a sequence of rock layers that become progressively older toward the center of the fold.
Therefore, if age relationships between various rock strata are unknown, the term antiform should be used.
Anticlines form many excellent hydrocarbon traps, particularly in folds with reservoir-quality rocks in their core and impermeable seals in the outer layers of the fold.

The progressing age of the rock strata towards the core and uplifted center, are the trademark indications for evidence of anticlines on a geologic map.
These formations occur because anticlinal ridges typically develop above thrust faults during crustal deformations.
The uplifted core of the fold causes compression of strata that preferentially erodes to a deeper stratigraphic level relative to the topographically lower flanks.
Motion along the fault including both shortening and extension of tectonic plates, usually also deforms strata near the fault.
This can result in an asymmetrical or overturned fold

A syncline is the opposite type of fold, having downwardly convex layers with young rocks in the core.

In anticlines, as seen on the ground, the oldest rocks are in the center of the fold.
In synclines, the youngest rocks are in the center of the fold.

Anticlines and synclines typically occur together.
Sharp folds are called «chevron» folds.

It is important to use the correct speed when transferring seismic data.
Anticlines appear wider on the unmigrated seismic sections beyond its true position and crosses through the reflections point.
The higher the dips, the wider the structure will appear on the unmigrated section.
On a migrated seismic section, an anticline appears compressed.
If the velocities use to migrate the data are incorrect, then the final migrated structure may be narrower or wider than the true structure.
This could lead to the wrong estimation of any oil or gas reserves underneath this anticline.
Also, incorrect migration velocities may lead to lateral and vertical uncertainties when using the seismic data to do well-to-seismic tie during seismic interpretation.