Integrated Science Unit 10, Chapter 28

28.3 Earthquakes As tectonic plates move, friction causes rock at plate boundaries to stretch or compress, this causes rocks to store energy. When the rocks break, change shape, or decrease in volume, the stored energy is suddenly converted to kinetic energy and an earthquake occurs.

28.3 Earthquakes A seismograph measures earthquakes, and seismologists use seismic waves to study Earth’s internal structure. This is similar to how a doctor uses X rays to look at bone structure.

28.3 Earthquakes The majority of earthquakes occur at the plate boundaries. Earthquakes also occur at a fault. Fault - a place crack in rocks along which movement occurs.

Earthquake Terms Epicenter – point on earth’s surface where the EQ waves touch surface first.

Northridge, California in January 1994. Focus – point inside crust where the EQ movement first occurred.

Seismic waves – common name given to all EQ waves. Hawaii earthquake damage

Worldwide Earthquakes Notice- most earthquakes occur on plate boundaries.

2 Categories of Seismic Waves Body & Surface

P waves Short for Primary waves Fastest and First body wave recorded by a seismograph Travel through solids and liquids (generate sound) Faster through more rigid material They are Compression waves Cause rock particles to move together and apart along the direction of the waves

P-Wave movement

S waves short for Secondary Waves Second body wave recorded by a seismograph Only travel through solids Can’t be detected on the side of the earth opposite the earthquake’s epicenter. They are Shear waves Cause rock particles to move up & down or side to side (right angle) to the direction in which the waves are traveling

S-Wave movement

Surface Waves Slowest moving wave & last to be recorded by seismograph Travel similar to ocean waves Cause the surface to rise, fall, turn and twist Very destructive: especially in loose earth

2 Types of Surface waves Love Waves Fastest kind of surface wave is called a Love wave , (named for A.E.H. Love, a British mathematician) Love worked out the mathematical model for this kind of wave in 1911. It moves the ground from side-to-side.

2 Types of Surface waves Rayleigh Waves Slower kind of surface wave (named for John William Strutt, Lord of Rayleigh Rayleigh predicted mathematically the existence of this kind of wave in 1885. It moves the ground up & down and side-to- side rolling the ground like waves on water. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves

Surface Waves movements

28.3 Earthquakes in the U.S. The west coast of U.S. experiences most earthquakes because of the San Andreas fault a boundary between Pacific and North American Plate, and the 10,000 + smaller faults. The Midwest and Eastern U.S. does experience EQ but they are more rare.

28.3 Earthquakes in the U.S. Minor earthquakes release stored energy in small, less destructive amounts. Rocks in areas that do not experience frequent small earthquakes may have a lot of stored potential energy. When this potential energy is finally converted to kinetic energy, the earthquake could be big.

28.3 Earthquake Safety Get outside to an open area (if possible), far from buildings and objects that could fall. Sit down to avoid falling. If you are inside: Drop, cover, and hold.

28.3 Preparing for Earthquakes A huge wave generated by an underwater earthquake or landslide is called a tsunami. The speed at which this wave travels can be about 700 kilometers per hour. (435MPH)

28.3 Earthquakes Key Question: What mechanical factors affect earthquakes? *Read text section 28.3 BEFORE Investigation 28.3