EarthquakesEarthquake

Footage

Epicenter• The point on Earth’s surface directly above where the

energy is released in an earthquake.• Focus = point where energy is released• Energy that reaches the surface is greatest at the

epicenter.

• Seismic Waves: Energy spreads outward in all directions as vibrations.

• Seismograph: Instrument that measures and records seismic waves.

• Seismogram: Seismic record, looks like jagged lines on paper.

Triangulation• Identifies the epicenter of an earthquake. • How?– Get records from 3 seismograph stations.– Plot circles on map from the records.– Find point where all 3 circles intersect.– That's the epicenter.

How to find the epicenter using triangulation

• Measuring time btwn arrival of P & S waves determines the distance btwn the seismograph & the epicenter.

Earthquake Waves• There are 3 types…

Primary (P) Waves Secondary (S) Waves Surface Waves

P and S waves explained

Primary (P) Waves• Move out from EQ focus• Travel fastest of the 3 waves• Move thru solid and liquid layers of Earth• PUSH and PULL rock, creating a back-and-forth

motion in the direction the wave is moving• Longitudinal wave

Secondary (S) Waves• Move out from EQ focus• Move slower than P waves• Only move thru solid rock• Move at right angles to P waves, causing rocks

to move UP and DOWN and SIDE to SIDE• Transverse wave

Surface Waves• Form when P and S waves reach the surface.• Can cause ground to shake, making rock sway

from SIDE to SIDE and ROLL like an ocean wave.

BRAINPOP Earthquakes