![]() The Piqiang Fault is a left-lateral fault. The unit of rock layers that moves toward the viewer relative to the red fault line is on the left. This method always works, no matter from which direction you are looking at the boundary!įigure 2.6.8. If it is on the left side, it is left-lateral. If the plate moving toward you is on the right side, the motion is right-lateral.Purple arrows show the direction the rock units (blue circles) are moving relative to a person looking down the red fault line. Based upon those displaced features, decide which rock unit appears to be moving toward you.Blue circles indicate distinctive rock units that have been displaced from one another by the fault. Find features that have been displaced apart from one another due to the sliding motion of the plates or rock units.įigure 2.6.6.The red color traces the fault line between rock units. Identify the boundary between the two rock units.įigure 2.6.5.To determine what type of transform fault it is, follow these steps: Google Earth imagery showing the transform Piqiang fault in China. For example, below is the Piqiang fault from China: Figure 2.6.4. How are these diagram different from the ones on Figure 2.6.2?Ī type of transform plate motion can be identified by examining the two tectonic plates from a bird’s-eye view. The different colors represent rock layers. Constructive plate boundary is one which two plates slide past one another thus neither creating nor destroying continental landmass. Figure 2.6.3 Block diagram and horizontal view of a transform fault. The different colors represent rock layers. Block diagram and horizontal view of a transform fault. Can you notice the difference? Figure 2.6.2. An examination of the two transform faults below demonstrates that they are very similar. However, these categories are not determined by the composition of the lithosphere. The motion at a transform fault is classified into two categories: right-lateral and left-lateral. Transform faults refer to the lateral displacement of large rock units due to the shearing motion caused by a transform boundary. Transform boundaries can cause both large faults and a series of smaller associated faults. Perhaps the most famous transform boundaries, however, are those on the continental lithosphere with effects that are directly felt by nearby cities and towns. Because the surrounding rock along the ridge is hard and brittle, it accommodates these shifts in spreading rates with sliding motions. They occur near these divergent boundaries because the spreading rate changes along a ridge. Most transform boundaries are associated with the spreading spreading centers at mid-ocean ridges. Although none of these events occur at transform boundaries, they are far from boring the continuous stress that builds within the lithosphere from the sliding motion causes faulting and earthquakes. No lithosphere is destroyed or created, and mountain chains are not built at transform boundaries. Shear stress operates at transform boundaries, which involves sliding motion. This motion does not create or destroy crust and will cause earthquakes, but no volcanoes.Ī transform boundary occurs when two tectonic plates move past one another. A transform boundary causes a fault between two plates of the lithosphere, which will slide past one another. Detailed studies of piercing points show the San Andreas Fault has experienced over 225 km of movement in the last 20 million years, and this movement occurred at three different fault traces.Figure 2.6.1. The best type of piercing point includes unique patterns that are used to match the parts of a geological feature separated by fault movement. ![]() Other types of faults-normal and reverse -tend to be more destructive, obscuring or destroying these features. Transform faults are unique because their horizontal motion keeps a geological feature relatively intact, preserving the record of what happened. Piercing points are very useful for recreating past fault movement, especially along transform boundaries. ![]() When a geological feature is cut by a fault, it is called a piercing point. The fault can be seen about halfway down, trending left to right, as a change in the topography. This is caused by the San Andreas Fault cutting roughly perpendicular to the creek, and shifting the location of the creek over time. Note as the creek flows from the northern mountainous part of the image, it takes a sharp right (as viewed from the flow of water), then a sharp left. \): Wallace (dry) Creek on the Carrizo Plain, California. ![]()
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