The Way Tectonic Plates Move earthquakes Turn on the speakers The Way Tectonic Plates Move

Learning Targets: Understand the anatomy of an earthquake – Elastic Rebound Theory Know the types of seismic waves 2 types of Body Waves 2 types of Surface Waves Understand the impacts of tsunamis

Earthquakes Earthquake: a sudden release of energy into the earth’s crust Almost constant small earthquakes 18 per year with 7 or greater magnitude 1 per year with 8 or greater magnitude Earthquakes are most often caused by the build up and sudden release of stress caused by the movement of tectonic plates. Which types of plate boundaries are prone to experiencing earthquakes? Convergent, transform, and divergent plate boundary.

Elastic Rebound Theory When stresses build, rocks bend elastically

Elastic Rebound Theory When stresses persist, energy continues to build in the rocks.

Elastic Rebound Theory When the stresses are greater than internal strength of rocks, the rocks snap or fracture.

Elastic Rebound Theory Although the rocks return to their original shape the stresses cause the rocks to move to a new position.

Elastic Rebound Theory This movement releases the energy that was stored in the rocks, which creates an earthquake

Focus and Epicenter Focus: place where rocks first move Can be anywhere from surface to 200 miles below ground Most earthquakes are shallow (6-10 mi) Why can’t earthquakes happen any deeper? High temperatures makes rocks plastic; no stress builds up The point where the rock ruptures is usually below the Earth’s surface. The point of rupture is called the earthquake’s focus.

Focus and Epicenter Epicenter: spot on surface above the focus Most shaking happens at epicenter Most damage may happen elsewhere 95% of epicenters are along plate boundaries This is how plate boundaries are drawn Just above the focus on the land surface is the earthquake’s epicenter

The point at which rock breaks, causing an earthquake, usually below the Earth’s surface is known as the focus. The point on the surface of the Earth that is directly above the focus of an earthquake is called the epicenter.

Earthquake Zones Pacific Ring of Fire Mediterranean-Asiatic Belt ~80% of all earthquakes Mediterranean-Asiatic Belt ~15% of all earthquakes Other plate boundaries and intraplate ~5%

Transform Plate Boundaries - Shear Stress Shallow earthquakes = more damage A lot of the energy goes to the surface Examples: San Andres, California Dead Sea, Jordan Chaman, Pakistan North Anatolian, Turkey Queen Charlotte, Alaska Forces that act in opposite but parallel directions causing two materials to slide past one another results in shear stress.

Convergent Plate Boundaries - Compression Stress Deep earthquakes Very powerful Volcanic activity Examples: Himalayas Aleutian Islands Andes Marianas and Mariana trench Cascades The stress that squeezes rocks together is compression.

Divergent Plate Boundaries Tension Stress Weak, shallow earthquakes New crust is thin Stress is released frequently Examples: Mid-Atlantic ridge Red Sea rift East Africa rift East Pacific rise Rocks being pulled apart are undergoing tension.

Seismic Waves Earthquake energy travels in seismic waves Study of seismic waves: seismology Body Waves: seismic waves that travel through the interior of the Earth Surface Waves: seismic waves that travel on Earth’s surface Seismic waves that travel along the surface of the Earth are known as surface waves. Seismic waves that travel through the solid body of the Earth are known as body waves. Seismo = Earth & -ology = the study of

Body Waves – P- & S- Waves 1. P-waves P = primary Fastest & first wave to be detected Can travel through solids, liquids, gases Compression waves A lot of power but not much damage done The fastest and first detected body waves after an earthquake are P-waves. The slower, more damaging body waves that are detected second after an earthquake are S-waves.

Body Waves – P- & S- Waves S = secondary Slower & second wave to be detected Motion produces Shear stress Only move through solids because liquids and gases have no shear strength S-shaped The fastest and first detected body waves after an earthquake are P-waves. The slower, more damaging body waves that are detected second after an earthquake are S-waves.

Surface Waves Cause most damage Surface waves travel along the ground outward from an earthquake’s epicenter. Slowest of all seismic waves.

Surface Waves – Love & Rayleigh Waves Love waves Side-to-side motion Like a snake

Surface Waves – Love & Rayleigh Waves Rolling motion Like ocean waves

Tsunamis Caused by underwater earthquakes Water is very heavy. One cubic yard of water weighs almost one ton (2000 lbs) Underwater earthquakes can result in massive ocean waves called tsunamis.

Power of water.

Tsunami 1