Unit 4 Earthquake Obj1 Describe Obj2 Describe Obj3 Describe Obj4 Describe Obj5 Describe Obj6 Describe prevented
11/10/14 5:13 PM
how stress causes earthquakes the types of faults and landforms created by earthquakes the types of seismic waves how earthquakes are measured how geologists monitor and predict earthquakes the damages caused by earthquakes and how it can be
Obj1 Describe how stress causes earthquakes • Earthquake: shaking and trembling result from movement of rocks beneath Earth’s surface. Caused by stress o Stress: force acts on rock to change its shape & volume. § Three types of stress: ú Shearing: Pushes rock in opposite parallel directions ú Tension: stretching rock, make it thinner in the middle ú Compression: squeezes rock together Obj2 Describe the types of faults and landforms created by earthquakes • Deformation: Any change in volume or shape of Earth’s crust • Friction: force opposes motion between surfaces o Low friction: rocks slide by each other o Moderate friction: sides jam together - from time to time jerk free o High friction: rocks lock together and do not move. o Stress increases until it is strong enough to overcome the friction force • Fault: a break in the Earth’s crust where movement happens. o Faults occur along plate boundaries, where forces of plate motion compress, pull, or shear crust so much that it breaks Three main types of faults: § Strike-slip Faults ú Shearing ú Rocks slip past each other sideways with little upor-down motion
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ú Occur along transform plate boundaries ú E.g. San Andreas fault Normal Faults ú Tension ú Hanging wall falls down in relation to foot wall ú Occur along divergent plate boundaries ú E.g. raft valley, Wasatch Mountain range - UTAH Reverse Faults ú Compression ú Hanging wall is pushed up in relation to foot wall ú Occur along convergent plate boundaries
E.g. Mountains Plateau is a large area of flat land elevated high above sea level. Some form when vertical faults push up a large, flat block of rock Folds: bends in rock/mountains when compression shortens and thickens crust. o Anticlines: fold bends upward into an arch o Syncline: fold bends downward in the middle to form a bowl o E.g. Worlds largest mountain ranges- Himalayas, Alps are fold mountain ranges. ú ú
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Obj3 Describe the types of seismic waves • Focus: the point beneath surface where rock breaks during earthquake • Epicenter: point on the surface directly above the focus • Seismic waves: vibrations travel through Earth carrying energy released during an Earthquake o carry energy away from focus, through interior, across surface. o Body waves: § P wave: primary wave, first waves to arrive. Longitudinal wave (compress and expand) § S wave: secondary wave, transverse wave o Surface waves: § Love wave: left / right
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Rayleigh wave: up / down, front / back, ocean wave like
Obj4 Describe how earthquakes are measured • Seismograph: record and measure vibrations of seismic waves • To tell how far the epicenter is from the seismograph, scientists measure the difference between the arrival times of the P waves and S waves. • Three circles are required to locate epicenter • Mercalli Scale: earthquake intensity measured by people’s experiences, scale 1-12. • Richter Scale: earthquake intensity measured by seismographs
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o accurate for small, nearby earthquakes; does not work for large or distant earthquakes Moment Magnitude Scale: measure energy released by the earthquake, most accurate for all earthquakes
• Obj5 Describe how geologists monitor and predict earthquakes • observe changes along faults o Creep Meters: monitors are placed on both sides of the fault to detect movement o Laser-Ranging Devices: Uses laser beams to detect even tiny fault movements. o Tiltmeters: measures tilting of the ground o Satellite Monitors: satellite bounces radio waves off the ground, as the waves echo back into space, the satellite records them. Can detect changes in ground movement • Geologists can determine earthquake risk by locating where faults are active and where past earthquakes have occurred. • Highest Risk: Along the pacific coast - California, Washington, Alaska Obj6 Describe the damages caused by earthquakes and how it can be prevented • Severe shaking o loose soil shakes more violently than surrounding rock.
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o a house built on solid rock will shake less than a house built on sandy soil. Liquefaction: an earthquake’s violent shaking turns loose, soft soil into liquid mud. o Requires shaking, water and loose soil o Use bedrock for foundation, instead of just soil / sand Aftershock: earthquake occurs after a larger earthquake in the same area. Tsunami: a large wave produced by an earthquake on ocean floor Building safety: o Base-isolation o Counter weight o Safe designs During earthquake: DROP, COVER, and HOLD!
