What are earthquakes?

Words to know Earthquake – Focus – Epicenter – Seismic Wave – a vibration of the earth (affects large area) the point where the earthquake starts the point on the earth’s surface directly above the focus energy sent out from an earthquake

Facts Most earthquakes occur along faults (where two plates touch) when potential energy is changed to kinetic energy. There are more than 3,000,000 earthquakes every year. = 8,000 a day = 1 every 11 seconds (According to the United States Geological Survey) Most of these are NOT felt by humans.

Earthquakes to know 1906 – San Francisco ~ 60 times more energy than the ’89 quake 1989 – San Francisco (Loma Prieta)

Notes There are 2 types of Seismic Waves 1.) Body Waves – Primary Waves (p-waves) Faster Travel through solid and liquid rock Travels as a longitudinal wave Secondary Waves (s-waves) Slower Travel through solid rock (not outer core) Travels as a transverse wave travel through earth’s body (interior)

Notes 2.) Surface waves – travel through the earth’s surface (crust) usually responsible for shaking the ground Sideways Wave Shakes the ground from side to side like a snake Up-and-Down Wave Can open and close cracks in the earth travel through the earth’s surface (crust)

How are earthquakes detected?

Words to know Seismograph – Seismogram – a device that is used to measure earthquakes the paper with the zigzag lines (created by a seismograph)

How are earthquakes measured?

Notes There are 2 scales used to measure earthquakes: 1.) Richter Scale very accurate because it uses a seismograph to measure the ground motion tells magnitude of earthquake on a scale from 1 – 10 (10 is largest magnitude) 2.) Mercalli Scale inaccurate because scale is based on eye witnessed destruction from earthquake scale in roman numerals from I – XII