![]() Blackwell Science Ltd., London.A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between.Įarth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults. Faults which move along the direction of the dip plane are dip-slip faults and described as either normal or reverse (thrust), depending on their motion. Faults which move horizontally are known as strike-slip faults and are classified as either right-lateral or left-lateral. Faults which show both dip-slip and strike-slip motion are known as oblique-slip faults. Most basins are hybrids of two or more of the several that exist. If geology were this simple it wouldn't really be a science. Note: The diagrams are crude and are only meant to convey the basic idea. The rock record in strike-slip fault zones shows that these basins open up and close frequently, every 10 million years or so, depending on the rate of movement on the fault. In arid environments this means that the rate of evaporation is greater than the rate at which water is added, leading to the concentration. Like the Dead Sea, these basins are often concentrated in salt or other solutes because they are generally isolated. In contrast to a regular lake-type sedimentation scheme, lateral changes in rock type ( facies) are closely spaced. The subsidence caused by these mechanisms is usually fast, and allows several kilometers of sediments to accumulate in just a few million years (which is a lot compared to most other sedimentary basins.) The sediments are usually coarse grained, or physically immature, since they generally travel a short distance to these basins. Chances are you ended up with one on top of another, with one bending slightly up and the other bending slightly down. To get an idea of why this happens, push two fingers together end to end until they move. The earth on one side is pushed up on one side and down on the other. ![]() They are often unusually deep, since the crust fractures brittly to about 10-15km to form the edges, and acts more ductile below these depths. These can range in size from a few kilometers to tens of kilometers in length and width. This is how the Dead Sea formed, as well as the Sea of Galilee, both lying on the same fault system. They are usually rectangular or rhombic when viewed from above. ![]() It's pretty easy to imagine this from the side, just a big old hole in the ground. liha explains left and right handed faults above. Whether a tensional or compressional stress is created depends on the direction of movement on the fault. This creates a basin where sediments can accumulate (also called the creation of accomodation space.) When there is a bend in a strike-slip fault, movement along the fault causes transtension or transpression. This very active right-lateral fault is over 1000 km (600 miles) long and creates devastating earthquakes due to the great friction that results from two plates moving past each other. ![]() North America's most famous strike-slip fault is the San Andreas Fault. So, along a right-lateral strike-slip fault, the rocks (and everything else) on the opposite side of the fault appear to have moved to the right:Īnd along a left-lateral strike-slip fault, the rocks (and everything else) on the opposite side of the fault appear to have moved to the left: Both topographic (such as mountains, valleys, and streams) and man-made (such as roads or fences) linear features can be offset to the right or left. ![]() This shearing horizontal movement can create distinct landforms such as linear valleys, lake chains, and sag ponds. Strike-slip faults occur along transform plate boundaries and involve horizontal movement of the fault blocks parallel to the strike of the fault. ![]()
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