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Earthquakes and Related Phenomena

Earthquakes and Related Phenomena. Earthquake Web Resources. http:// earthquake.usgs.gov /. Deadliest Earthquakes on Record. Introduction to Earthquakes. M s Earthquakes/year 8.5 - 8.9 0.3 8.0 - 8.4 1.1 7.5 - 7.9 3.1 7.0 - 7.4 15 6.5 - 6.9 56

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Earthquakes and Related Phenomena

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  1. Earthquakes and Related Phenomena

  2. Earthquake Web Resources http://earthquake.usgs.gov/

  3. Deadliest Earthquakes on Record

  4. Introduction to Earthquakes MsEarthquakes/year 8.5 - 8.9 0.3 8.0 - 8.4 1.1 7.5 - 7.9 3.1 7.0 - 7.4 15 6.5 - 6.9 56 6.0 - 6.4 210 • ~1 million earthquakes a year • Change of 1 Mw = ~30 X energy • Great earthquakes; Ms >8 • Major earthquakes; Ms=7-7.9 (widespread damage) • Moderate earthquakes: Ms=6 (considerable damage) • Population factors: density, land use, and building construction

  5. Where do earthquakes occur? Plate boundaries, but not only – intraplate earthquakes are also common

  6. Earthquake Occurrence • Most occur along plate boundaries. • Loma Prieta (1989) • North Ridge (1994) • Intraplate earthquakes • Can be large and quite damaging. • New Madrid zone is a foundered rift zone • Salt Lake City and south into New Mexico • Charleston, S.C.

  7. Largest US Earthquakes

  8. Relationship of Earthquakes to Faults

  9. Earthquake Processes • Faults, Folds & Concealed Faults, and Movement • Fractures • Faults are fractures or systems along which rocks have been displaced • Model: brick -bungee cord on a winch; sand paper • Joints are fractures and fractures systems along with rocks have NOT been displaced • Slip rate aver. long-term rate of movement ( mm/yr or m/1000 yrs); risky measurement • Seismic waves produced by rupture • Faults-seismic sources; used to evaluate the earthquake risk in a given area

  10. Earthquake Processes • Fault types • Strike-slip faultsonly have horizontal displacement (right-or left-lateral) • Normal faultsoccur where the hanging wall moves down with respect to the foot wall; results in crustal extension • Reverse faultsoccur when the hanging wall moves up with respect to the foot wall; results in crustal shortening; low fault plane angle ( less than 45°)= thrust fault • Oblique faultshave both horizontal and vertical components • Buried faultsmay cause earthquakes and have to surface expression

  11. Faults – Understanding Strike and Dip

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