Sixth Grade Science Unit 1 Lesson 6

Seismic Waves are the result of tectonic plate movements under the surface of Earth.

First there is a disturbance or movement of the plates at the plate boundaries. We call the location of this first disturbance the FOCUS.

The space between the plate boundaries is called the FAULT.

The EPICENTER is a point directly above the FOCUS on the surface of Earth. It is used by scientists for measurement purposes.

Seismic waves are vibrations caused by the energy released in a plate movement event.

The seismic vibration waves will radiate out from the focus in all directions.

There are two kinds of Seismic Waves that we are going to study. P waves S waves

S Wave

Surface wave Transverse wave Moves perpendicular to its forward motion Will only travel through a solid

P Wave Compression wave Longitudinal wave Molecules of wave move together and apart as the wave moves forward Wave refracts as it moves through materials with different densities

P waves travel much faster than S waves and always reach recording stations first.

S waves P waves

Wave Movements

Different Wave Movements

Shadow Zone is an area where neither P nor S waves go

To find the exact location of an earthquake, scientists triangulate the data collected at earthquake tracking stations Triangulation of Wave Data

Circles are drawn around each of three reporting stations at the distance the earthquake was detected. The point at which the three circles Intersect is the EPICENTER. TRIANGULATION

Parts of a Wave

More About Waves

Still More About Waves

Wave Parts Crest - top of wave Trough – bottom of the wave Wavelength – measurement from one crest to the next Frequency – number of waves that pass a fixed point in a given period of time Amplitude - height of wave from crest to point of equilibrium