Warmup 1. What is an earthquake’s location on a surface called? 2. What is an earthquake’s location underground called?

7.3 Earthquakes

Earthquakes Earthquake- The shaking of the Earth’s crust cause by rapid displacement of rocks, usually along a fault.

Epicenter- the point on the Earth’s surface directly above the focus of an earthquake. Focus- the point within the crust where an earthquake originates

Earthquake Waves

Body Waves P-waves (primary or push-pull waves)- they cause back-and- forth motion in the same direction as the wave is traveling S-waves (secondary or shear waves)- they cause motion at right angles to the direction in which the wave is traveling

Surface Waves L-Waves (love or long waves)- travel along the Earth’s surface at slow speeds back and forth R-Waves (Rayleigh waves)- travel along the Earth’s surface similar to an ocean wave

Measuring Earthquakes 8

Seismic Waves- energy waves set in motion by an earthquake Seismograph- an instrument used to record seismic waves

Paths of Body Waves P-waves travel faster than S- waves Seismic waves travel faster through denser materials Seismic wave bend (refract) as they move from a medium of one density into a medium of a different density S-Waves will not travel through Earth’s outer core (which is liquid)

Earthquake Strength

Locating Epicenters Find difference in travel time between P and S Waves Use table to determine “distance from epicenter” for 3 seismograph stations Epicenter is located where 3 circles intersect

Faults Compression – the type of stress that occurs when an object is squeezed, such as when 2 tectonic plates collide. Tension- the force (stress) that occurs when forces act to stretch an object.

Folding- the bending of rock layers due to stress Two main types of folds: Anticlines- upward arching folds Synclines- downward troughlike folds

Fault- the surface along which rocks break and slide past one another. 2 Main types of faults: Normal faults- occur at divergent boundaries Reverse faults- occur at convergent boundaries