7.1 Stress in Earth’s crust Turn on the speakers The Way Tectonic Plates Move
Learning Targets Describe the anatomy of an earthquake and relate plate tectonics (different types of plate boundaries) to earthquakes. Describe how stress builds up earthquakes
Stress Earthquake = removal of stress Plate movement is never smooth Plates made of solid, rough rock Stress builds up at plate boundaries Fold - Rocks bend Fracture - Rocks break Earthquake = removal of stress Where is the energy stored before an earthquake occurs. In the rocks. What kind of energy is that? Potential Energy
Stress Mantle convection cells puts a lot of stress on the rocks of the lithosphere. Where does the heat come from to create mantle convection cells? Inner and outer core True/False The mantle is semi liquid. Must be liquid for convection to occur. If mantle was completely solid, only conduction.
Types of Stress Confining: pressure from all directions No deformation Compression: pushed together Fractures or folds Tension: pulled apart (extension) Stretch or break Shear: parallel but opposite (scissors) Break and slide past one another
Types of Stress What type of plate boundary Confining - Results from being buried Compression - Convergent Tension -Divergent Shear - Transform
Elastic vs. Plastic Rocks under stress will deform Elastically: bend then return to original shape Rocks under more stress will deform Plastically: bend without the ability to return to the original shape When too much pressure is applied to a rock it may change shape. If the rock returns to its original shape after the pressure is removed, the rock is said to have bent elastically. When too much pressure is applied to a rock it may change shape. If a rock is deformed permanently and does not return to its original shape after the pressure is removed, the rock is said to have bent plastically.
Geologic Structures Folds Joints Faults
Geologic Structures - Folds Folds: bends in rock due to compression Monocline: non-horizontal layering Anticline: Upward bulge Syncline: Downward bulge When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.
A simple bend in the rock layers so that they are no longer horizontal but are inclined. Oldest rocks at the bottom, youngest are at top.
Fold that arches upward Fold that arches upward. The oldest rocks are found at the center and the youngest are draped over them at the top. When rocks arch upward to form a circular structure, a dome. If the top of the dome is eroded off, the oldest rocks will be exposed at the center.
Fold that bends downward Fold that bends downward. The youngest rocks are at the center and the oldest at the outsides. When rocks bend downward in a circular structure, that structure is called a basin.
Both anticline (left) and syncline (right)
When rocks bend downward in a circular structure that structure is called a basin.
Miniature basin
Geologic Structures - Joints Joints: breaks where rocks do not move When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.
Joints – When there is a block of rock still standing on either side of a fracture line
Geologic Structures - Faults Faults: breaks where rocks have moved When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.
Fracture – If the stress continues, the rock will break Fault If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault. Fracture – If the stress continues, the rock will break
Types of Faults: Dip-slip & Strike-slip Slip is the distance rocks move along a fault. Types of Faults: Dip-slip & Strike-slip
Geologic Structures Summary Folds: bends in rock due to compression Monocline: non-horizontal layering Anticline: Upward bulge Syncline: Downward bulge Joints: breaks where rocks do not move Faults: breaks where rocks have moved When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.