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Over 2000 years Aristotle: earthquake as subsurface wind 19th century: scientific observation begins Understanding: what, why, where, magnitude, frequency Earthquakes (seisms): caused by rapid release of energy Caused by: volcanic activity, meteors, landslides, explosions Also caused by: sudden movements along faults Faults: Sharp lines in rock layers Stresses in near-surface rocks, rocks fracture, shift along fault Rock rupturing produce shock waves Concentrated energy release, moves radially outward Fault mapping: determine earthquake-hazard belts

4: Earthquake History

Google Images, FaultsBlue Anchor, Somerset, UK

Understanding Earthquakes, (2:55)

Hutton’s Unconformity, Scotland

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Plates move: mountains elevated, basins warped

down Lithospheric rocks fracture, i.e. jointing, cracking Large stress: fault, tilting, folding Dip-Slip Fault: vertical movement caused by

pulling or pushing force Normal fault – pull apart, sea floor spread centers Reverse fault – compression, convergence,

subduction, continental collisions Strike-Slip: horizontal movement along fault Ex. Queen Charlotte Transform Fault: horizontal movement on

boundary Plate sides move past each other

Types of Faults

Google Images, Queen Charlotte Fault

Earthquakes of the Midwest, (12:53)

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Surface waves – complex motion, slowest velocity Primary (P) waves – compressional motion, fastest Secondary (S) waves – “shake” motion, slower than

P waves Travels through solids Focus – inside earth where waves originate Epicenter – point on surface above focus Earthquake destruction determined by: Intensity, duration, building material, structural design Destruction results from: Ground shaking, liquefaction, tsunami, landslides Ground subsidence and fires

Earthquake Waves

Reconstruction of a Cascadia Subduction, (14:33)

Fig 8.16: Damage 1964 Anchorage, Alaska

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Def: fractures in rocks with displacement Normal fault (fig): caused by tensional

forces Hanging wall below fault surface, footwall

above Prevalent along spreading centers Crust fractures into blocks Ex. Basin and Range Province Produced parallel mountain ranges Due to movement along fractures

Fault Specifics

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Type of dip-slip fault Hanging wall block moves up Due to strong compressional forces Accommodates crustal shortening

Reverse and Thrust Faults

Mountains fault, (1:25)

Google Images: Thrust Fault

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Transform fault: large strike-slip fault Cuts through lithosphere Occurs at boundary between plates

Transform Fault

Google Images: San Andreas Fault

San Andreas Fault, (3:03)