The growth faults in the region strike N15E, have steep dips (~70 deg), and vertical displacements of 1–4 mm/yr. The current transtensional state generates normal growth faults and some strike slip motion. Displacement on the fault is approximately 6 cm/yr. The Salton Trough is an active pull-apart located in a step-over between the dextral San Andreas Fault and the Imperial Fault. Pull-apart basins are amenable to research because sediments deposited in the basin provide a timeline of activity along the fault. Examples įamous localities for continental pull-apart basins are the Dead Sea, the Salton Sea, and the Sea of Marmara. Transtensional settings are believed to generate greater surface subsidence than pure-strike slip alone. Recent sandbox models have shown that the geometry and evolution of pull-apart basins varies greatly in pure-strike slip situations versus transtensional settings. The tectonic subsidence of strike-slip basins is mainly episodic, short lived (typically less than 10 Ma), and end abruptly with commonly very high tectonic subsidence rates (greater than 0.5 km/Ma) compared to all other basin types.

Connecting the tips of step over faults to the opposite fault are bounding basin sidewall faults. This is illustrated in the accompanying figures.Ī regional strike slip fault is referred to as a principle displacement zone (PDZ). įor example, two overlapping left lateral fault must have a left-step-over to create a pull-apart basin. The step-over or bend in the fault must be the same direction as sense of motion on the fault otherwise the area will be subject to transpression. Pull-apart basins form in extensional to transtensional environments along fault bends or between two adjacent left-lateral faults or two right-lateral faults. Bends and step-overs of adjacent faults become favorable locations for extensional and compressional stress or transtension and transpression stress, if the shear motion is oblique. The inhomogeneity and structural complexity of continental crust causes faults to deviate from a straight course and frequently causes bends or step-overs in fault paths. Mechanics and fault configuration Diagram of a pull-apart basin redrawn from Frisch et al. Pull-apart basins are also referred to as overlapping-tension-zones (OTZ). Dimensionally, basins are limited to the distance between the faults and the length of overlap. Frequently, the basins are rhombic or sigmoidal in shape. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend creates an area of crustal extension undergoing tension, which causes the basin to sink down. In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments.

Transform vs strike slip fault