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Folds, Faults & Earthquakes Rocks under stress can either bend or break both are referred to as deformation Any str PowerPoint Presentation
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Folds, Faults & Earthquakes Rocks under stress can either bend or break both are referred to as deformation Any str

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Folds, Faults & Earthquakes Rocks under stress can either bend or break both are referred to as deformation Any str
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  1. Folds, Faults & Earthquakes Rocks under stress can either bend or break both are referred to as deformation Any stress can deform rocks compressional (squeezing) = folded rocks anticlines and synclines extensional (stretching) = “thinned” beds Whether or not the rocks fold or break depends on the amount of stress, the strength of the rock and the duration and rate that the stress is applied to the rocks

  2. Folded Rocks - syncline = U-shaped fold Folded Rocks - syncline

  3. Anticline = A-shaped fold (in this case cut in half by a river

  4. Large scale folding in the Appalachian Mountains

  5. If the stress is applied too fast or if it greatly exceeds the rock strength… the rocks break => releasing the stored energy The break is called a fault, the energy released is called an earthquake Small earthquakes are cool- everyone feels them, no one gets hurt, minimal damage Big ones suck. They collapse buildings and other structures that kill people and create secondary events that do the same

  6. Significant Earthquakes Significant Earthquakes Y ear Location Magnitude Deaths 1964 USA (Alaska) 8.6 131 1970 Peru (Chimbote) 7.8 25,000 1971 USA (San Fernando, California) 6.6 65 1975 China (Haicheng) 7.3 ? 1976 Guatemala 7.5 23,000 1976 China (Tangshan) 8.0 242,000 1985 Mexico (Mexico City) 8.1 9,500 1988 Armenia 7.0 25,000 1989 USA (Loma Prieta, California) 7.1 63 1990 Iran 7.3 40,000 1992 Turkey 6.8 570 1992 USA (Landers, California) 7.5 1 1992 Egypt 5.9 500+ 1993 India 6.4 30,000+ 1994 USA (Northridge, California) 6.7 61 1994 Bolivia 8.2 ? • 13 million+ lives have been lost in the past 4000 • 13 million+ lives have been lost in the past 4000 years due to earthquakes and related phenomena. years due to earthquakes and related phenomena.

  7. Earthquakes Shaking caused by the sudden release of energy in the Earth, resulting from displacement of rock along a fault. • • • • Most are caused by faults associated with plate movement. Fault- a break in the lithosphere that moves Epicenter- a projection of the location on the Earth’s Surface Focus- the location of the energy release (rupture) along the fault

  8. Relationships between a fault plane, epicenter, focus, and energy waves

  9. Look for relative motion-helps determine how force was applied Vertical Faulting Lateral Faulting HW is a normal fault Opposite block moves right means right lateral HW is a reverse fault Head on Headwall Feet on Footwall Fault Plane

  10. Fault type tells us something about motion, stress and forces needed to create them and thus gives hints as to plate tectonics setting Normal fault = extensional force Reverse fault = compressional force Lateral fault = shearing force

  11. What statement is most accurate concerning earthquakes? The stronger the earthquake, the more people are killed. All earthquakes occur close to a tectonic plate edge. The poorer the country, the more deaths are likely to occur due to moderate to severe earthquakes Earthquake epicenters are always associated with faults at Earth’s surface

  12. Seismic Waves (1:3) Seismic Waves (1:3) • cause shaking and destruction. • cause shaking and destruction. • Two types of seismic waves: • Two types of seismic waves: Body Waves travel through the Body Waves travel through the • • Earth. Earth. Surface Waves travel only along Surface Waves travel only along • • the surface of the Earth the surface of the Earth Lab exercise using P- and S-waves to locate an earthquake

  13. Body Waves Body Waves Primary Waves (P-waves) Primary Waves (P-waves) • • • • travel fastest travel fastest • • move through solid, liquid or gas. move through solid, liquid or gas. • • P-waves are compressional. P-waves are compressional. Secondary Waves (S-waves) Secondary Waves (S-waves) • • • • travels slower than P-waves travels slower than P-waves • • solids only! solids only! • • S-waves S-waves - shear waves that move material - shear waves that move material perpendicular to their direction of travel. perpendicular to their direction of travel.

  14. Surface Waves Surface Waves Rayleigh Waves (R-waves) Rayleigh Waves (R-waves) • • the slower of the surface waves. the slower of the surface waves. • • • Love Waves (L-waves) • Love Waves (L-waves) • • move similar to S-waves move similar to S-waves • • displacement of material occurs in a displacement of material occurs in a horizontal plane perpendicular to direction of horizontal plane perpendicular to direction of wave movement. wave movement.

  15. Movie clip

  16. Seismograph Seismograph • An instrument that measures and records earth movements produced by an earthquake.

  17. Time-Distance Graphs Time-Distance Graphs • The time difference between P- and • The time difference between P- and S-waves arrivals allows calculation S-waves arrivals allows calculation of the distance from the epicenter. of the distance from the epicenter. Dt = d {(Vp-Vs)/(VpVs)} solve for d where Dt = Time interval between arrival of P and S waves at a station measured from seismograms D = distance of station from epicenter Vp ; Vs = velocity in Km/sec of P waves and S waves - generally Vp = 6.0 km/sec; Vs = 3.5 km/sec * making the (Vp-Vs)/(VpVs) term = (2.5/21) = 0.119 * Within 1000 km

  18. Graphical version of the distance calculation.

  19. Time-distance • Time-distance graphs only tell graphs only tell us how far we us how far we are from the are from the epicenter. epicenter. • Triangulation • Triangulation of three stations of three stations allows us to allows us to pinpoint the pinpoint the epicenter. epicenter. • Using three seismograph locations Using three seismograph locations the location can be pinpointed on a the location can be pinpointed on a map map Triangulation Triangulation • • Location of earthquakes Earthquake website

  20. Earthquakes and Plate Margins Earthquakes and Plate Margins

  21. A seismic hazard map

  22. Exceptions to Exceptions to Plate Boundary Plate Boundary earthquakes 'quakes New Madrid, MO • in 1811 and 1812 a series • in 1811 and 1812 a series of strong intraplate of strong intraplate earthquakes occurred near earthquakes occurred near New Madrid, MO. New Madrid, MO. • • Only twenty people died (imagine the toll if this (imagine the toll if this occurred in the region occurred in the region today), and the quake was today), and the quake was felt in Boston, 1600 km felt in Boston, 1600 km away. away.

  23. Focal Depth & Plate Boundary Type Focal Depth & Plate Boundary Type Focal depth increases in a "Benioff Zone" adjacent to deep ocean • trenches that define convergent boundaries. Benioff zone

  24. Categories-Depth Categories-Depth • Shallow-focus: • Shallow-focus: • • focal depth less than 70 km. focal depth less than 70 km. • Intermediate-focus: • Intermediate-focus: • • focal depth between 70 and 300 km. focal depth between 70 and 300 km. • Deep-focus: • Deep-focus: • • focal depth greater than 300 km. focal depth greater than 300 km. • most earthquakes (~80%) occur at • most earthquakes (~80%) occur at depth of less than 100 km. depth of less than 100 km.

  25. Movie clip

  26. Earthquake Intensity & Magnitude Earthquake Intensity & Magnitude Intensity (qualitative data) Intensity • • • • A measure of earthquake damage. • MMI - scale (Modified Mercalli Intensity) • MMI - scale (Modified Mercalli Intensity) - - ranges from 1 to 12, expressed as roman numerals (I, II, III, IV) ranges from 1 to 12 - - observation of damage, semi-independent of energy released observation of damage • • Magnitude (quantitative data) Magnitude • • a quantitative measure of the amount of energy released a quantitative measure of the amount of energy released by an earthquake. by an earthquake. - - measured on the Richter Scale- max energy in one instant measured on the Richter Scale- max energy in one instant - - each step is multiplied by a factor of 30 • Moment magnitude is energy released over the entire area • overthe entire time

  27. Earthquake Prediction Earthquake Prediction • Short term predictions are still unsuccessful. • Short term predictions are still unsuccessful. • Long term forecast maps are more reliable • Long term forecast maps are more reliable offer a magnitude and probability of • offer a magnitude and probability of • occurrence for a given interval of time occurrence for a given interval of time • Damage maps are developed based on • Damage maps are developed based on intensity of past earthquakes and current intensity of past earthquakes and current geologic maps. geologic maps.

  28. Tsunamis and Ground failures Tsunamis and Ground failures • Seismic sea-waves • Seismic sea-waves • produced by earthquakes on the sea floor. • produced by earthquakes on the sea floor. • Travel at very high speeds • Travel at very high speeds • 100's of km/hr in the open ocean • 100's of km/hr in the open ocean - Barely noticeable in open ocean - Barely noticeable in open ocean • but may reach heights of 65 m as they near shore. • but may reach heights of 65 m as they near shore. Mass movements Mass movements • Earthquake-triggered • Earthquake-triggered landslides cause much landslides cause much damage in mountainous damage in mountainous areas. areas. • 1959 Madison County • 1959 Madison County (Montana) earthquake (Montana) earthquake

  29. Notice the P- waves and S-waves traveling outward from the focus Movie clip