Landward-Dipping Fault

Synonym of Counter-Regional fault. However, it must be said that all faults belonging to a Counter-Regional System are landward-dipping faults, but not all landward-dipping faults are belong a Counter Regional System. See: Counter Regional System.

Lateral Confining Pressure

Pressure induced laterally by a tectonic stress (t). Indeed, when a tectonic stress (t) is added in one direction it produces, by reaction, a lateral confining pressure (h). The amount of lateral confining pressure is function of rocks' rheology and ranges from 5/10 to 10/10 of the tectonic stress. On the vertical, towards the free surface, the tectonic stress (t) is released by uplift or subsidence.

At a given depth point, the weight of the sediments (v) creates a lateral pressure (h). At normal depths, the lateral pressure ranges between 5/10 and 8/10 of the vertical pressure. However, at greater depths, as the biaxial ellipsoid becomes uniaxial, the values of the lateral pressure becomes equal to the vertical pressure.

Leading Edge

The foremost edge of a spreading salt body, in surface or under water, i.e., the forward part of the moving salt.

On this seismic line, the leading edge of the allochthonous salt nappe is easily recognized by the associated bathymetric anomaly. The autochthonous salt layer is underlined by the tectonic disharmony recognized at around 7 seconds.

Lessening Tectonic Regime

Extensional tectonic regime developed when the tectonic stress is not big enough to balance the geostatic pressure in the effective stresses ellipsoid. This tectonic regime, characterized by a 1 vertical and 2 and s3 horizontal, occurs in association with folded-belts and foredeep basins.

This tectonic regime is often recognized in the distal part of foredeep basins. Indeed, in this areas, extensional structures generally half-grabens and grabens strike perpendicular to the compressional structures of the fold-belts, i.e., cylindrical-folds and thrusts.

Level of Neutral Buoyancy

Depth at which the bulk density of the overburden is equal to that of salt (about 2200 kg/m3). This is the level at which a diapir spreads most rapidly if surrounded a yielding, fluid overburden (including air or water). Terrigeneous clastics must be buried before they compact, dehydrate, or cement to reach the density of the salt. This burial depth varies from basin to basin but is approximately 450 to 900m under normal compaction gradients (hydrostatic pore pressure) and around 500m where shales are under-compacted (pore pressure elevated between hydrostatic and lithostatic pressure gradients).

Listric Fault

A particular curvilinear faults having a normal fault geometry up-dip and a reverse fault geometry down-dip, as in a slumping fault. In spite of the fact that listric comes from "listron", in Greek, means "spoon", presently, listric fault is used to express all kinds of fault having a curvilinear geometry.

Listric faults as the one illustrated on this seismic line develop mainly in slope environments. Indeed, due to the seaward increasing of the water depth, slope failures take place up-dip. The up-dip extension is balanced by a sedimentary shortening created by local compressional tectonic regime developed near the toe of the slope.

Lithostatic Pressure

See: Geostatic Pressure.