How and where are earthquake waves detected and recorded?A seismograph is an instrument

that records earthquake waves.It is also used to determine the

magnitude of an earthquake the location of its epicenter.

Anatomy of Earthquakes

A seismograph designed to record vertical ground motion

A seismograph designed to record horizontal ground motion

Typical Seismogram

Seismograph measuring horizontal displacement

Compressional Wave (P-Wave) Animation

Particle motion consists of alternating compression and dilation(enlargement & reduction). Particle motion is parallel to the direction of propagation (longitudinal). Material returns to its original shape after wave passes.

Shear Wave (S-Wave) Animation

Particle motion consists of alternating transverse motion. Particle motion is perpendicular to the direction of propagation. Transverse particle motion shown here is vertical but can be in any direction

Surface Wave (L-Wave) Animation

Particle motion consists of alternating transverse motions. Particle motion is horizontal and perpendicular to the direction of propagation (transverse).

Seismology

Types of seismic waves Body waves

Travel through Earth’s interior Two types based on mode of travel Primary (P) waves Push-pull (compress and expand) motion, changing

the volume of the intervening material Travel through solids, liquids, and gases Generally, in any solid material, P waves travel about

1.7 times faster than S waves

Seismology

Types of seismic waves Surface waves

Travel along outer part of Earth Cause greatest destruction Waves exhibit greatest amplitude and slowest velocity

Waves have the greatest periods (time interval between crests)

Often referred to as long waves, or L waves

Seismology

Types of seismic waves Body waves

Secondary (S) wavesShake" motion at right angles to their direction of

travel Travel only through solids Slower velocity than P waves Slightly greater amplitude than P waves

Locating the source of earthquakes

Terms Focus - the place within Earth where

earthquake waves originate Epicenter – location on the surface

directly above the focus Epicenter is located using the difference in

velocities of P and S waves

Draw the diagram on page 215 and write down the information on each caption.

What is the relationship between particle density and seismic wave?How and where are Earthquakes recorded? (page 217)Summarize how the magnitude of an earthquake is measured.

A time-travel graph is used to find the distance to the epicenter