12ESS Earthquakes

Earthquake

The shaking that results from the sudden movement of rock beneath Earth's surface.

Fault

A fracture in the earth's crust

Fault Scarp

An exposed cliff created by movement along a fault.

Focus

The point beneath Earth's surface where rock breaks under stress and causes an earthquake

Epicenter

the point on the Earth's surface directly above the focus of an earthquake

Footwall

The block of rock that forms the lower half of a fault

Hanging wall

The block of rock that forms the upper half of a fault.

Elastic energy

energy stored inside a rock when it is stretched or compressed until it breaks

Kinetic energy

Energy released when a rock reaches its elastic limit and fractures

Elastic limit

Maximum force a rock can withstand before it fractures

Friction

A force that opposes motion between two surfaces that are in contact

Compression

Stress that squeezes rocks together until they fracture

Tension

Stress that pulls rock apart until it fractures

Shear

Stress that builds up between two slabs of rock moving in opposite directions

Normal Fault

A type of fault where the hanging wall slides downward; caused by tension in the crust

Reverse Fault

a type of fault where the hanging wall slides upward; caused by compression in the crust

Strike Slip Fault

a type of fault where rocks on either side move past each other sideways with little up or down motion; caused by shear stress in the crust

Seismic Waves

Vibrations that travel through Earth carrying the energy released during an earthquake

P waves

Body wave that causes particles of rock inside the Earth to move in a back-and-forth direction. Can travel through solids and liquids. These arrive first.

S waves

Body wave that causes particles of rock inside the Earth to move up and down. Can only travel through solids. These arrive second.

Love waves

Surface waves that shear the ground in a horizontal direction. Can only travel through solids. Third to arrive.

Rayleigh waves

Surface waves that travel in a backward-rotating, elliptical motion, causing both vertical and horizontal ground movement. Can travel through solid, liquid, and gas. Fourth to arrive. Dangerous.

Seismograph

A device that records ground movements caused by seismic waves as they move through Earth

Liquefaction

When unconsolidated sediment settles and compacts during earthquake shaking, and water in the spaces between sediments gets pushed to the surface.

Richter Scale

A scale that rates an earthquake's magnitude based on the size of its tallest seismic wave. The bigger the wave's amplitude the more energy the earthquake has released.

Moment Magnitude Scale

A scale that rates earthquakes by estimating the total energy released by an earthquake at its focus point.

Modified Mercalli Intensity Scale

A scale from I to XII used to rate earthquakes based on the amount of observed damage they cause.

Magnitude

Measure of the energy released during an earthquake