earthquakes movement & destruction. what is an earthquake? shaking of the earth produced by a...
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Earthquakes
Movement
&
Destruction
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What is an Earthquake?
• Shaking of the Earth produced by a sudden movement of rock beneath its surface
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How Do Earthquakes Occur?Elastic Rebound Theory
• Deformation builds up and causes crust to bend
• When strain exceeds strength of the rock, it will “snap” into a new position
• In the process of rupturing, energy is released in the form of “seismic waves”
• Elastic strain energy is stored
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Where Do EQ Occur?• Faults
– Fracture in the Earth’s crust where one side moves with respect to another
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Types of Fault
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Fault Terminology
– Fault block above the fault – Fault block below the fault
• Footwall• Hanging wall
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Normal Fault
• Hanging wall moves down relative to the footwall• Exhibits lengthening or extension of the crust• Associated with fault block mountains
– Basin and Range
– Horst – uplifted block– Graben – down dropped block
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Basin and Range
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Reverse Fault
• Hanging wall moves up relative to footwall• Exhibits shortening or compression of crust• Have dips > 45° • If dip’s < 45°, then thrust fault
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Strike-Slip Fault
• Horizontal displacement
– Right lateral – As you face the fault, opposite side of plate moves right
• Types of Strike Slip:
– Left lateral – opposite side of plate moves left
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San Andreas Fault
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Destruction from EQ
• Ground Shaking
• Tsunami
• Fire
•Liquefaction
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Destruction from EQ Ground Shaking
• Rapid horizontal movement of ground may shift homes and cause them to collapse
• Shaking is exaggerated in water-saturated or weak sediment
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Northridge, CA – 1994M=6.7; 61 killed
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Destruction from EQTsunami
• Giant Sea Waves generated by submarine EQ’s
•Tsunamis travel 1,000’s of miles•Waves may reach 15 m (50 feet) in
height and travel up to 960 km/hr (600 mph)
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Alaska - 1964
• M = 9.2; 125 died (110 tsunami, 15 EQ)
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Alaska, 1964
• There was so much uplift that once-submerged areas were exposed after EQ
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Indonesia 2004
• M=9.0; 280,000 killed
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Destruction from EQ’sFires
• Many gas lines may break from the severe shaking
• Unfortunately, many water lines may break as well so that firefighting becomes impossible
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San Francisco - 1906
• M = 7.8; 3,000 killed
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Destruction from EQ’sLandslides
• Mountains usually form in areas of convergent boundaries• The steep slope are prone to landsides when shaken• Landslides are common following EQ’s in California
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Northridge - 1994
• Landslides prevalent in Santa Susana Mountains
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Destruction from EQ’s Liquefaction
•Occurs when water-saturated is reorganized due to violent shaking
•Sediment collapses, expelling water, and causes the ground to subside
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U.S. Earthquake Hazards
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San Andreas Fault
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Southern California Seismicity
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Southern California Faults
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Earthquake Predictions