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Earthquakes Natural vibrations of Earth’s ground caused by: - Movement along tectonic plates -OR -Volcanic eruptions Forces Within Earth Fracture caused when: -the forces acting on the Earth’s Crust exceed the strength of the Crust and Rocks The Deformation of material caused by: -Stress In the Forms of: - Compression - Tension - Shear • Earthquakes occur at the boundaries of tectonic plates. • See a lot of EQ’s in places like Japan and California. • FACT: 3 million earthquakes happen every year! Faults • A fault is the fracture or system of fractures along which movement occurs. • The surface along which the movement takes places is called the fault plane. Types of Faults Types of Faults • Reverse faults are fractures that form as a result of horizontal compression. • Normal faults are fractures caused by horizontal tension. • Strike-slip faults are fractures caused by horizontal shear. • When rocks break during an earthquake energy is released in the form of seismic waves. • These waves travel in all directions. • Focus is the exact point within the earth where the rock first breaks. • Epicenter is the point on the surface immediately above the focus. Waves spread out as a wave travels. 3 types of waves associated with an EQ p-wave s-wave surface wave P-WAVE • primary wave • longitudinal type wave • fastest wave: 6 km/sec Longitudinal S-WAVE • secondary wave • transverse wave • ½ speed of a p-wave: 3 km/sec • they do not travel through liquids Transverse Transverse Waves • A wave that causes the particles of the medium to vibrate perpendicularly to the direction the wave travels. SURFACE WAVE • they travel along earths surface • it’s the wave you “feel” during an earthquake • up/down and back/forth motion • slowest of all 3 waves Surface Waves • Occurs in a liquid • Circular particle motion Surface Waves • Occur at the boundary of two different mediums such as water and air. Surface Waves cont • Surface waves have a rolling pattern of particle motion. Raleigh Waves • Occurs in solid rock • Particles move in elliptical path
