Seismic Waves

Earthquake Waves

óWhen fault slips, released energy travels outward in seismic waves ¡Outward from point on fault that first

slipped: focus (or hypocenter) ¡Epicenter is point on surface of Earth

directly above focus

Types of Earthquake Waves óFirst arrival is P wave ¡Primary ¡Compressional motion ¡Feels like sudden jolt ¡Travels at 5-8 km/s through rock ¡Sometimes heard as low rumbling

Types of Earthquake Waves óSecond arrival is S wave ¡Secondary ¡Shear motion ¡Feels like wiggling, difficult to stand ¡Travels at 3.5-4.5 km/s through rock ¡More destructive than P waves ¡Do not travel through liquids ¡Both P and S waves are body waves

Types of Earthquake Waves

ó Last arrivals are surface waves ¡Include Love and Rayleigh waves ¡Travel along surface of Earth and fade

downward ¡Long, rolling motion ¡Travel slower than P or S waves ¡Can be more destructive than P or S waves

Seismic Wave Videos

óP-wave óS-wave óRaleigh wave óLove wave

Types of Earthquake Waves óWave terminology ¡Period: time for one complete cycle between

successive wave peaks to pass ¡Wavelength: distance between wave crests ¡Amplitude: amount of positive, negative wave

motion ¡Frequency: number of peaks per second

Fig. 3-19, p. 45

Seismographs

§ Seismographs record shaking of earthquake waves on seismograms § How do we stand still and watch the Earth move? § Heavy weight suspended from rigid column anchored to ground:

stays still from its own inertia while ground moves

§ Pen attached to weight marks paper attached to ground

§ North-south, east-west and vertical components

Fig. 3-20, p. 45

Figure 3-21a p45

Figure 3-21b p45

Figure 3-21c p45

Earthquake-Wave Velocities ó Surface waves travel with constant velocity through

shallow rocks: arrival times increase linearly with distance ó P waves and S waves travel faster as they go deeper through the Earth: waves at greater depths reach seismograph along curving paths

LIKE RIPPLES ON WATER

Content Objectives

óStudents will be able to: ¡Explain that seismic waves propagate outwards

as wave fronts from the source in 3-dimensions (X, Y, & Z axes) and have a velocity

¡Explain that the amplitude of seismic waves is related to the amount of energy released from the source and decreases with distance from the source

¡Compare and contrast seismic waves to ripples on water.

Videos

óLike ripples óUnlike ripples óUSA array tutorial óNevada earthquake animation USA

array óMid-Indian-Ocean earthquake

animation USA array

Human Wave Demonstration

óObjective Students will: ¡Model how earthquake waves travel at

different speeds ¡Construct a distance and time graph to

represent the P and S waves ¡Visualize why s-waves do not travel

through liquids

óVIDEO: The Human Wave

Seismic Waves and the Slinky

óSlinky demonstrations of ¡P-waves ¡S-waves ¡Surface waves óVIDEO óSeismic Slinky