Chapter 19 Notes Earthquakes

Stress and Strain Earthquakes occur when stress builds up and causes movement in the Earth’s crust Compression: squeezing forces Tension: pulling forces Shear: opposing parallel forces/twisting Elastic deformation: initial response to stress plastic deformation occurs under high stress just before breaking

Faults Normal fault: produced by tension forces Reverse fault: produced by compression forces Strike-slip fault: produced by shear forces

Earthquake Waves Body Waves Primary (P-waves): compression waves; move parallel to the direction of wave motion Secondary (S-waves): transverse waves; move at right angles to the direction of wave motion Surface waves: move sideways and up and down

Earthquake Waves P-waves move fastest Surface waves are slowest, last the longest, and are the most destructive

Earthquake location Focus: the origin of the EQ waves Epicenter: “above” the center

Earthquake Measurement Seismometer: an instrument that records EQ waves Seismogram: the record of EQ waves

Time travel curves The difference in arrival time of the P-waves and S-waves can show how far the waves have travelled.

Clues to Earth’s Interior EQ waves are reflected and refracted in different ways by the different materials inside the Earth

Measuring Earthquakes Richter Scale: measures magnitude energy released numeric scale (no true upper limit) Modified Mercalli Scale: measures intensity based on the amount of damage Roman numerals I to XII

Richter Scale

Mercalli Isoseismic Map

Locating an Earthquake The P-wave and S-wave arrival times determine the distance a station is to an EQ Three stations are required to locate the epicenter of an EQ

Seismic Belts Circum-Pacific and Mediterranean-Asian belts

Earthquake Hazards “Earthquakes don’t kill people, buildings do.” Structural failures Brittle building materials cause more damage Building height oscillations Land and soil failure Soil liquefaction Tsunami Ocean wave generated by sea floor movement

U.S. Earthquake Risk