BJU Earth Science Chapter 6

Accelerometer

Sensors that measure changes in speed, such as the shakes produced by earthquakes

Seismometer

An instrument that measures earth waves

Earthquake

A series of low frequency shock waves traveling through the earth

Stress

A measure of force exerted within an object

Compression

A force being pressed down onto an object

Tension

Taking slack out of a flexible object-as in pulling on a rope in tug-of-war.

Shear

Exists when forces are acting in opposite directions on different parts of the same object

Divergent Boundaries

The plate sections of the earth that move apart

Convergent Boundaries

The plates that move toward each other

Transform Boundaries

Places where plates slide past each other in opposite directions along long cracks in the crust.

Strain

The distortion, bending, stretching, or compression of a material under stress.

Joints

Cracks in rocks

Fault

Occurs when the sections of rock on opposite sides of the crack move relative to each other

Fault Plane

The smooth surface between two pieces of a broken rock

Strike

The direction of a fault

Dip

The angle of the fault face downward from the horizontal

Dip-Slip Fault

A fault's motion that is parallel to its dip (up and down).

Normal Fault

When the block above the faults surface drops in relation to the block under the fault

Reverse Fault

Upper block rises in relation to lower block

Strike-Slip Fault

When the motion along the fault is horizontal

Lubricants

Oil, grease, and other substances used to reduce friction

Locked Fault

Builds up shear stresses, as the adjacent plates continue to move slowly

Aftershock

Secondary earthquakes

S Waves

The second type of waves to arrive at a seismic station

P Waves

The fastest body waves

Body Waves

waves that pass right through the earth

Focus

Hypocenter

Epicenter

Spot of the earths surface directly above the focus

Richter Scale

A scale that measures the strengths of earthquakes

Magnitude

Indicates the energy released by the earth movement

Intensity

A measure of how much damage that actually results from the earthquake

Modified Mercalli Intensity (MMI)

The earthquake destructiveness scale

Ductility

ability to be drawn into a wire

Brittle

characteristic of hard minerals that are easily fractured

Elasticity

stretchiness of a mineral, most important property for earthquakes

Mountain ranges

Location of most Earthquakes in the U.S.

Seismograph

seismometer with a recording device

Seismogram

a recording made with a seismograph

Amplitude

Height of a wave

Frequency

speed of a wave

Tsunami

large ocean wave created by seismic waves

Seismic gap

when an area prone to earthquakes has not had one for a period of time