Plate Tectonics

Last 30 Days Earthquakes

Physical Features

Last 30 Days Earthquakes with Plate Boundaries

Earth’s Structure

Earth’s Layers Core: Inner Core: Center of the earth, solid ball of metal (Nickel and Iron), hottest layer Outer Core: Liquid layer that surrounds the solid inner core, mostly Iron, some Nickel, causes the earth’s magnetic field Mantle: Largest layer (84% of Earth), “plastic like fluid” (pliable), made of lighter elements Crust: Hard outermost layer, made up of continental and oceanic crust Lithosphere: Made up of upper mantle and crust, divided into tectonic plates

Tectonic Plates

Do the plates move? Alfred Wegener (1910) noticed the shape of the continents fit together like puzzle pieces. Evidence: Fossils and mountain ranges on opposite sides of oceans He couldn’t explain how the continents moved

New evidence Age of oceanic crust Magnetic alignment Since then, scientists have discovered the mechanism that drives the plate movements: Convection

How does a lava lamp work? Convection current: The rising and sinking movement of a liquid or gas (but NOT a solid) due to changes in density Warm materials are less dense Cool materials are more dense

Plate Movement

Types of Crust Oceanic Crust Continental Crust Plate Boundary Made of basalt Thinner More dense Continental Crust Made of granite Thicker Less dense Plate Boundary Where two tectonic plates meet Convergent When plates come together Divergent When plates move apart Subduction When the more dense plate turns downward and sinks into the mantle

Plate Boundary Types Convergent Divergent Transform Where two plates move towards each other (collision) Divergent Where two plates move away from each other Transform Where two plates grind past each other

Convergent Boundaries Oceanic-Oceanic Older, colder crust subducts under the other oceanic crust Melting of the subducted crust occurs and magma rises, forming a volcano (island arc) Example: Japan, New Zealand, Aleutian Islands

Convergent Boundaries Oceanic-Continental Oceanic crust ALWAYS subducts under continental crust (more dense) Melting of the subducted crust occurs and magma rises, forming a volcano Example: Andes Mountains, Cascade Mountains

Convergent Boundaries Continental-Continental Continental crust is buoyant, so neither plate subducts The crust thickens, forming mountain ranges and high plateaus on both sides of the mountains Intense pressure and heat cause metamorphic rocks to form within the thickened crust Example: Himalayan Mountains

Divergent Boundaries Two plates are moving away from each other in opposite directions  Oceanic Divergent Boundary Magma rises and erupts from long cracks called Mid-Ocean Ridges New crust forms along ridges and older crust moves outward towards continents Example: Mid-Atlantic Ridge

Divergent Boundaries Continental A convection current under continental crust (sometimes a hotspot) causes spreading A Rift Valley forms Spreading continues, seawater enters Ridge continues spreading, ocean forms Example: Red Sea, African Rift Valley

Transform Boundaries Where plates are sliding past each other Lithosphere is neither created nor destroyed Examples: San Andreas, most transform boundaries occur in mid-ocean ridges where spreading rates are not the same

Faults Fault: a fracture in the Earth’s crust Foot wall Hanging wall Each type of plate boundary is associated with a type of fault: Convergent ---→ Thrust/Reverse Faults Divergent ---→ Normal Faults Transform ---→ Strike Slip

Thrust/Reverse Faults Compression stress Associated with Convergent boundaries Hanging wall moves up, foot wall moves down When movement along a fault is the reverse of what you would expect with normal gravity we call them reverse faults! Examples: Himalayan Mountains

Normal Faults Tension (extension) stress Associated with Divergent boundaries Hanging wall moves down, foot wall moves up When movement along a fault is the normally what you would expect with normal gravity we call them normal faults! Examples: Wasatch Fault

Strike Slip Sheering Stress Associated with Transform boundaries Slip past each other with little up and down motion Examples: San Andreas, zig zags in Mid-ocean Ridges Strike Slip Fault