Earthquakes
An earthquake is the shaking and trembling that results from the movement
of rock beneath Earth's surface.These forces are example of stress, a force that acts on rock to change its shape or volume.Shearing, tension, and compression work over millions of year to change the shapeand volume of the rock.Stress that pushes
a mass of rock in two opposite directions is called shearing.The stress forces called
compression squeezes rock until it folds or breaks. Any changes in the volume or shape of Earth's crust is called deformation. A fault is a break in the crust where slabs of crust slip past each other.Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks. In a srtike slip fault, the rocks on either side of the fault slip past each other sideways with little up or dwon motion. In a normal fault, the fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault. The half of the fault that lies above is called the hanging wall The half of the fault that lies below is called the foot wall. A rivers fault has the same structure as a normal fault, but the blocks move in the opposite direction. Over millions of years, faults movement can change a flat plain into a towering mountain range.When normal faults uplift a block a rock, a fault block mountain forms. Folds are bends in rock that form when compression shortens and thickens part of earths crust. A fold in a rock that bends upward into an anticline. A fold in rock that bends downward in the middle to form a bowl is a syncline.A plateau is a large area of flatland elavated high above sea level.
