Chapter 19

Elastic Deformation

Causes materials to bend and stretch; proportional to stress so if the stress is reduced or returns to zero the strain or deformation is reduced or disappears

Strain

Deformation of materials in response to stress

Stress

Forces per unit area that act on a material-compression tension and shear

Fault

Fracture or system of fractures in Earths crust that occurs when stress is applied too quickly or stress is too great

Seismometer

Instrument used to measure horizontal or vertical nation during an earthquake

Tsunami

Large powerful ocean wave generated by the vertical motions of the seafloor during an earthquake

Magnitude

Measure of the energy released during an earthquake which can be described using the richter scale

Modified Mercalli Scale

Measures earthquake intensity on a scale from 1-12

Richter Scale

Numerical rating system used to measure the amount of energy released during an earthquake

Plastic Deformation

Permanent deformation caused by strain when stress exceeds a certain value

Seismic Gap

Place along an active fault that has not experienced an earthquake for a long time

Focus

Point of the initial fault rupture where an earthquake originates that usually lies at least several kilometers beneath earths surface

Epicenter

Point on earths surface directly above the focus of an earthquake

Soil Liquefaction

Process associated with seismic vibrations that occur in areas of sand that is nearly saturated

Seismogram

Record produced by a seismometer that can provide individual tracking of each type of seismic wave

Moment Magnitude Scale

Scale used to measure earthquake magnitude taking into account the size of the fault rupture the rocks stiffness and amount of movement along the fault using values that can be estimated from the size of several types of seismic waves

Primary wave

Seismic wave that squeezes and pushes rocks in the same direction that the wave travels

Secondary wave

Seismic waves that causes rock particles to move at right angles to the direction of the wave known as an S wave

Amplitude

That size of the seismic waves

Seismic wave

The vibrations of the ground during an earthquake