Earth Structures
Lesson Goal: Recognize how bedrock responds to tectonic forces originating deep within Earth. Compare and contrast stress and strain. In material science, strain is express by deformation caused through the action of stress on a physical body. It is calculated by a change in two body states; beginning and final states. The difference in two states expresses the (numerical) value of strain. Strain is equal to a change in size and shape of a physical body. Strain can be categorized in to two types; homogenous and non-homogenous.
Homogenous strain is referred if the strain is equal the entire portion of the body while non-homogenous strain; the strain is equal to a portion of a body. Stress is equivalent to force per unit area. It is calculated by the intensity of internal forces performing within a body across imaginary internal surfaces. This results to externally applied and body forces. Stress is related to force while strain is related to deformation. In stress-associated properties, all materials have temperature dependent differences.
Static fluids support the hydrostatic pressure; it will flow under shear stress. Moving viscous fluids supports the dynamic pressure (Samaniego “Stress, strain and fault patterns”). Distinguish between joints and faults. What makes a fault active? In geology, joint is a fracture in a rock mass, which has no offset. It refers to non-lateral movement of one side relative to the other while a fault refers to a fracture in rock mass where one side slides laterally past to the other. The structure of a joint forms a solid and hard rock that stretches past its elastic modules.
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In any case, the rock fractures in a plane perpendicular to the extensional stress is paralled with compressive stress. Joints naturally exist when erosion removes overlying rocks. This reduces the compressive load and allowing the rock to expand laterally. In addition, cooling of hot rock masses and cooling joints forms joint. There are three major classifications of faults. These include normal, reverse and strike slip faults. The (tectonic) stresses due to plate motions were developed over time and breaks in the crust of the Earth. The rocks at uneven periods break up.
This results to earthquakes. Normal faulting originated at the divergent boundaries while reverse faulting originated at convergent boundaries. Normal faulting is associated with crustal extension while reverse faulting is associated with crustal shortening. Lastly, strike-slip faulting originated at transformed boundaries (Reches “Faulting of rocks in three-dimensional strain fields. Theoretical analysis”). Explain what each type of unconformity implies about the sequence of geologic events. Four types of unconformity include; disconformity, nonconformity, angular unconformity and paraconformity.
Disconformity refers to an unconformity between parallel layers of sedimentary rocks representing a period of erosion. Nonconformity exists between sedimentary rocks and igneous rocks. The sedimentary rock lies above and deposited on the pre-existing and eroded igneous rock. Unconformity refers to a break in the continuity of sedimentary rocks caused by erosion. Paraconformity appears when the beds above and below are parallel; no erosion-al surface is present. In any case, the unconformity results to a separation and/or deposition of two rock masses causing the sequence of geologic events.
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