When rocks bend downward in a circular structure, that structure is called a basin Figure below. If the rocks are exposed at the surface, where are the oldest rocks located? Basins can be enormous. This is a geologic map of the Michigan Basin, which is centered in the state of Michigan but extends into four other states and a Canadian province. A rock under enough stress will fracture. If there is no movement on either side of a fracture, the fracture is called a joint , as shown in Figure below.
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Granite rocks in Joshua Tree National Park showing horizontal and vertical jointing. These joints formed when the confining stress was removed from the granite. If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault Figure below.
Sudden motions along faults cause rocks to break and move suddenly. The energy released is an earthquake. Slip is the distance rocks move along a fault. Slip can be up or down the fault plane. Slip is relative, because there is usually no way to know whether both sides moved or only one. Faults lie at an angle to the horizontal surface of the Earth. The dip defines which of two basic types a fault is. There are two types of dip-slip faults.
In normal faults , the hanging wall drops down relative to the footwall. In reverse faults , the footwall drops down relative to the hanging wall. This diagram illustrates the two types of dip-slip faults: normal faults and reverse faults. Imagine miners extracting a resource along a fault. The hanging wall is where miners would have hung their lanterns.
High School Earth Science/Stress in the Earth's Crust - Wikibooks, open books for an open world
The footwall is where they would have walked. A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults Figure below. At Chief Mountain in Montana, the upper rocks at the Lewis Overthrust are more than 1 billion years older than the lower rocks.
How could this happen? Normal faults can be huge. They are responsible for uplifting mountain ranges in regions experiencing tensional stress Figure below. A strike-slip fault is a dip-slip fault in which the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. Figure below.
Imagine placing one foot on either side of a strike-slip fault. One block moves toward you. If that block moves toward your right foot, the fault is a right-lateral strike-slip fault; if that block moves toward your left foot, the fault is a left-lateral strike-slip fault. It is a right-lateral strike slip fault Figure below. People sometimes say that California will fall into the ocean someday, which is not true. Two converging continental plates smash upwards to create mountain ranges Figure below.
Stresses from this uplift cause folds, reverse faults, and thrust faults, which allow the crust to rise upwards.
Subduction of oceanic lithosphere at convergent plate boundaries also builds mountain ranges Figure below. The Andes Mountains are a chain of continental arc volcanoes that build up as the Nazca Plate subducts beneath the South American Plate. When tensional stresses pull crust apart, it breaks into blocks that slide up and drop down along normal faults.
High School Earth Science/Stress in the Earth's Crust
The result is alternating mountains and valleys, known as a basin-and-range Figure below. Skip to main content. When plates press against each other, one plate's edge is pressed downward by the compression as the other plate's edge rides over it. These subduction zones appear as deep ocean trenches, usually facing mountains -- the protruding edge of the overriding plate.
12.1 Stress and Strain
In many places, such as the Pacific Ocean's "Ring of Fire," the material of the sinking crust interacts with the hot mantle below, causing lines of volcanoes such as those found in the Aleutian Islands, the Andes, and the Cascade Range of the western United States. Crustal plates pulling apart from each other, or fracturing, under tension can develop rift valleys as seen in East Africa.
Crust fills the developing gaps in the form of basalt, which can flood the surface to form a basaltic sill. In the mid-oceanic ridges in the Atlantic and Pacific oceans, molten basalt released under the water hardens into pillow-like blobs, creating new oceanic crust.
Hydrothermal vents release hot, mineral-laden water, which resembles black smoke.
In some cases, the edges of the plates slide past each other, neither significantly pressing together, nor pulling apart. Here the movement causes a lateral shear. Where movement causes horizontal displacement, it is called a "strike-slip" fault.
The movement isn't smooth; the plates build up stress which eventually releases in a sudden movement, causing earthquakes like the San Fransisco event. The San Fransisco earthquake provides a vivid example of dangers arising from crustal movement.