EARTHQUAKES CAUSES AND CHARACTERISTICS Earthquakes 101 National Geographic

EARTHQUAKES CAUSES AND CHARACTERISTICS

Earthquakes 101 • National Geographic • https: //www. youtube. com/watch? v=V Sg. B 1 IWr 6 O 4&feature=youtu. be

What is an earthquake? An earthquake is a shaking of Earth’s lithosphere when rocks suddenly shift, releasing stored energy.

Seismology • Seismology is the study of earthquakes. • Scientists who study earthquakes are called seismologists.

Why do Earthquakes happen? • When plates interact, huge amounts of force is place on the rock. • Pressure builds up on the rock causing stress. • Stress is the amount of force per unit area that is placed on an object.

Stress can cause deformation • Most of the time friction between plates prevents movement along the plate boundary. • Stress can cause the rock to deform (change shape).

Folding • When a small amount of stress is put on a rock slowly, the rock can bend, causing rock to fold.

Types of Deformation. • Plastic deformation is when rock remains folded when the pressure is taken away. • Elastic deformation occurs when rock goes back to its original size and shape when the pressure goes away.

Elastic-Rebound Theory • Eventually the stresses become great enough to overcome the friction and the plates move, causing an earthquake. • Elastic rebound is when rock breaks and snaps back to its original shape before the deformation.

Faults • When rock is put under so much stress that it can no longer bend, it may break, forming a fault.

Where do earthquakes occur? • Earthquakes occur where tectonic plates meet. • 80% of all earthquakes occur in the Pacific Ring of Fire.

Earthquakes at Divergent Boundaries: • As the plates pull apart, the crust stretches, and the crust breaks along faults. • Most crust at divergent boundaries is thin and weak therefore only a little bit of pressure builds up before the rock breaks making earthquakes here small.

Earthquakes at Divergent Boundaries

Earthquakes at Convergent Boundaries • The pressure when plates come together grows and grows until the rock breaks. • The earthquakes at convergent boundaries can be very strong because there is so much pressure. • The strongest earthquakes ever recorded have all happened at convergent boundaries.

Earthquakes at Convergent Boundaries

Earthquakes at Transform Boundaries • As the plates move past each other, pressure builds up until the rock breaks and the plates slide past each other along a fault.

Earthquake Zone • A place where there a lot of faults is called an earthquake zone. • The San Andreas Fault Zone in California is an example of an earthquake zone. • Most earthquake zones are near plate boundaries, but some are in the middle of tectonic plates

Parts of an Earthquake Focus and Epicenter

Earthquakes Focus – the location below the surface where the energy is released. Epicentre – point on the surface directly above the focus Fault Epicenter Seismic waves move out in all directions from the focus. Seismic waves Focus

• Earthquakes occur at various depths, depending on the plates involved. • Earthquakes near the surface tend to cause more damage.

Homework • Read p 271 - 273 • Answer questions from p 273 • #1 -3

3 Types of Folds: • Synclines - the oldest rocks are found on the outside of the fold. Most synclines are U-shaped. • Anticlines - the youngest rocks are found on the outside of the fold. -shaped. • Monoclines - rock layers are folded so that both ends of the fold are horizontal.

Fault Block • The blocks of rock that are on either side of the fault are called fault blocks. • When fault blocks move suddenly, they can cause earthquakes.

Hanging Wall and Footwall • When a fault forms at an angle, one fault block is called the hanging wall and the other is called the footwall.

Normal Fault • In a normal fault, the hanging wall moves down, or the footwall moves up, or both. • Normal faults form when rock is under tension. • Tension is stress that pulls rock apart. • Therefore, normal faults are common along divergent boundaries, where Earth’s crust stretches.

Reverse Fault • In a reverse fault, the hanging wall moves up, or the footwall moves down, or both. • Reverse faults form when rock is under compression. • Compression is stress that pushes rock together. • Therefore, reverse faults are common at convergent boundaries.

Strike-Slip Fault • In a strike-slip fault, the fault blocks move past each other horizontally. • Strike-slip faults form when rock is under shear stress. • Shear stress is stress that pushes different parts of the rock in different directions. • Therefore, strike-slip faults are common along transform boundaries.