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Understanding Faults and Earthquakes

Learn about the different types of geologic forces, faults, plate tectonic stresses, seismic waves, earthquake waves, earthquake magnitude, damage caused by earthquakes, liquefaction, and volcanic activity in the Ring of Fire.

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Understanding Faults and Earthquakes

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  1. Faults & Earthquakes These can be either constructive or destructive forces 3 basic types of geologic forces 1. Tension: pulling force ← → 2. Compression: pushing force → ← 3. Shearing: forces sliding past each other in opposite directions. ↑↓

  2. Fault: a fracture in earth’s crust where movement occurs 3 types of Faults: 1. Normal (tension) fault: one side drops in relation to the other. 2. Reverse (compression) fault: one side pushes up in relation to the other. 3. Strike-Slip (shear): fault: horizontal shift in opposite directions.

  3. PLATE TECTONIC STRESSES • Plate boundaries and faults (= cracks where plate sections are moving in different directions) cause friction as plates move • Plates in a fault zone have STICK-SLIP motion • Periods of no movement (stick) and fast movement (slip) • Energy stored as plates stick, • Energy released as plates slip

  4. EARTHQUAKES sudden movement or shaking of the Earth • Caused by plate tectonic stresses • Located at plate boundaries & faults within plates • Resulting in breakage of the Earth’s brittle crust • https://www.youtube.com/watch?v=CtBXTvtFaCU&nohtml5=False (2 ½ minute earthquake video)

  5. SEISMIC WAVESproduced by the release of energy • move out in circles from the point of rupture (focus) • Types of waves: surface & body(travel inside & through earth’s layers) • - P waves: longitudinal – compression (back and forth movement of rock) arrives 1st; travels thru solid, liquid, gas • S waves: sideways (transverse – shear) movement of rock; travel thru solids only; arrives 2nd. • L waves (surface): when both P & S waves reach the surface

  6. EARTHQUAKEWAVES • Seismographs record earthquake waves • Seismograms show: Amplitude of waves • (how much rock moves or vibrates) • - Distance to the epicenter - • Earthquake direction • How to read a Seismograph: • - P & S (body waves) move • through earth & arrive first. • P & S waves used to calculate magnitude of • earthquake. • - Amplitude = height of wave (how much the rock moves; size of vibration)

  7. EARTHQUAKE WAVES • FOCUS = place deep within the Earth and along the fault where rupture occurs • EPICENTER = geographic point on surface directly above focus • The epicenter is determined by taking seismic readings from at least 3 stations are taken and circles drawn from those stations based on time intervals from those stations. • The point where all circles intersect is the epicenter. This also referred to as Triangulation. https://www.youtube.com/watch?v=694yaY2ylTg&nohtml5=False (locating the epicenter vide o (3 1/2 minutes)

  8. EARTHQUAKEMAGNITUDE measures the size of seismic waves  the energy released by the earthquake • Richter scale=measurement of energy released based upon wave amplitude (size of vibration) • <2 to ~10 • Amplitude of wave goes up by 10 (Logarithmic scale) • What you need: • Amplitude (size of vibration = wave height) • Time between arrival of 1st P and 1st S waves

  9. Mercalli Scale: Measures the intensity of an earthquake based on qualitative data (damage to man-made structures) MERCALLI VS. RICHTER

  10. ISOSEISMIC MAPS • Connects areas of with the same Modified Mercalli number • Areas are colored according to Modified Mercalli number Loma Prieta Earthquake 1989 show the distribution of intensities

  11. EARTHQUAKE DAMAGE • Most caused by SURFACE waves (arrive last) • Landslides • Building damage • Liquefaction

  12. LIQUEFACTION The process that occurs during earthquakes when loose soil particles (sand and soil, not bedrock) turn into a watery, slurry mix as a result of the seismic vibrations. • Results in a loss of soil strength & the ability of the soil to support weight • https://www.youtube.com/watch?v=4Uwxr42JqYQ (liquifaction video 2 ¼ minutes) • (liquifaction video 2: 1 ½ minutes) https://www.youtube.com/watch?v=536xSZ_XkSs

  13. Most volcanoes and earthquakes occur in the ring of fire, an area circling the Pacific Ocean. • New Madrid fault is an area of active earthquake activity in the American mid-west. • A Tsunami is a giant tidal wave often caused by an underwater earthquake. http://video.nationalgeographic.com/video/101-videos/tsunami-101 (Tsunami video 2 ¾ minutes)

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