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Earthquakes Earthquakes • Result from abrupt movements on faults or fractures in the Earth’s lithosphere – Energy is slowly accumulated in rocks – Two plates slide past one another – Parts of plates stick because of friction – As the rest of the plate continues to slide, more friction energy is created. Seismic waves • Focus – point where first seismic waves begin (center of earthquake) • Epicenter – point on Earth’s surface directly above focus. Waves • Waves – vibrations that move outward from focus (“center” of earthquake) – 2 types of waves • 1. Body waves – travel though Earth’s interior -Primary waves (P-wave): highest velocity, first to be detected -Secondary waves (S-wave): travel slower and are detected afterwards • 2. Surface waves – travel on Earth’s surface P Wave S Wave Surface Waves • The two surface waves are Love (L) waves and Raleigh waves. • L-waves cause the ground to move side to side. • R-waves roll like an ocean wave causing the ground to go up and down Measuring Earthquakes • Seismograph – measures and records vibrations of a earthquake. • Information displayed on a Seismogram – Distance vs. time graph – P wave faster than S wave Seismogram Using the Seismogram • The distance between the beginning of the first P wave and the first S wave tells you how many seconds the waves are apart. • This number will be used to tell you how far your seismograph is from the epicenter of the earthquake. • Using three seismographs, a map and a compass, the epicenter can be located. Locating the epicenter of an earthquake Richter Magnitude Scale • Developed by Charles Richter • Scale that assigns a single number to quantify the amount of seismic energy released by an earthquake. • Base-10 logarithmic scale, which means an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0. Effects • Intensity is a measure of the damage caused by an earthquake. • It is measured by a number on the modified Mercalli scale. • The drawbacks are unreliability and differing factors like building materials, distance from quake, foundation of the buildings, opinions of people, etc. • • • • • • • • Effects of earthquakes include: Shaking and ground rupture Landslides and avalanches Fires Soil liquefaction Tsunami Floods Human impacts
