EARTHQUAKES &

SEISMIC WAVESCHAPTER 6.2

WHAT IS AN EARTHQUAKE?

The shaking and trembling that results from the movement of rock beneath Earth’s surface

Caused by plate movement

WHERE DOES AN EARTHQUAKE START?Focus: area beneath Earth’s

surface where rock that is under stress breaks, triggering an earthquake

Epicenter: point on the surface directly above the focus

HOW DOES AN EARTHQUAKE MOVE?Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.

ARE THERE DIFFERENT TYPES OF SEISMIC WAVES?

YES!

P WAVESFirst waves to arriveCompress and expand the ground

like an accordionCrust vibrates forward and back

along the path of the waveCan damage buildingsTravels through solids and liquids

S WAVESSecondary wavesSeismic waves that vibrate from side to side as well as up and down

Cannot travel through liquidsShakes structures violently

Moves like an accordion

Moves like ‘the wave’ at a football game

SURFACE WAVESMove more slowly than P waves and S waves, but can produce severe ground movements

Can make the ground roll like ocean waves or shake buildings from side to side

HOW ARE SEISMIC WAVES MEASURED?

With a SEISMOGRAPH

WHAT ARE THE 3 WAYS TO MEASURE AN EARTHQUAKE?1. Mercalli scale: rates the earthquakes according to level of damage at a given place (pg 191)

MERCALLI SCALE XII IN LA PAZ, BOLIVIA

2. Richter Scale: rating of an earthquake’s magnitude based on the size of the earthquake’s seismic waves

Magnitude of an Earthquake: a # that geologist assign to an earthquake based on the earthquake’s size

3. Moment Magnitude Scale: rating system that estimates the total energy released by an earthquake

GEOLOGISTS USE THE SEISMIC WAVES TO LOCATE AN EARTHQUAKE….

EPICENTER