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Shaking of Earth’s crust by a release of energy. Earthquakes Cause / Location • Friction prevents plates from sliding (where plates meet…fault) strain builds up strain overcomes friction plates move suddenly releasing ENERGY!!! • Focus: point of 1st movement • Epicenter: point on Earth’s surface directly above focus. Rows of lettuce in CA in 1979. Displaced by an earthquake. Earthquake (Seismic) Waves • P waves: – – – – – Primary waves (Get to you 1st) Fastest (about 6km/sec) Compressional waves Squeeze and stretch rock Can travel though solid and liquid material. • S waves: – Secondary waves – About 3km/sec – Material moves at right angles to the direction in which the wave is traveling – Can travel through solid material, but not through liquids. • Surface Waves: – P and S waves produce surface waves – About 1.5 km/sec – 2 types: • Love waves: material moves from side to side • Rayleigh wave: material moves in elliptical patterns. Seismograph • Detects and records waves produced by earthquakes – Can pick up activity thousands of miles away • Use data to locate earthquakes’ epicenters and to measure their magnitudes • About 10,000 stations around the world Seismogram Summarize! • Foci and epicenters • 4 wave types and notable characteristics • P- and S-wave shadow zones (where and why) • Seismographs and seismograms