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ESYS 150 LECTURE 8 EARTHQUAKES IN WESTERN N AMERICA

ESYS 150 LECTURE 8 EARTHQUAKES IN WESTERN N AMERICA. North America History: 85 Ma to Present, Subduction Zone Earthquakes Alaskan Trench Middle America Trench Cascadia Subduction Zone Spreading Center Earthquakes.

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ESYS 150 LECTURE 8 EARTHQUAKES IN WESTERN N AMERICA

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  1. ESYS 150LECTURE 8EARTHQUAKES IN WESTERN N AMERICA North America History: 85 Ma to Present, Subduction Zone Earthquakes Alaskan Trench Middle America Trench Cascadia Subduction Zone Spreading Center Earthquakes

  2. NORTH AMERICA 85 MA TO PRESENTAge determined from magnetic anomaliesOverlap isochrons to reconstruct position of plates

  3. NORTH AMERICA 85 MA TO PRESENTPACIFIC PLATE/NORTH AMERICA PLATE

  4. NORTH AMERICA 38MA - PRESENTDEVELOPMENT OF SAN ANDREAS FAULT

  5. NORTH AMERICA 20MA - PRESENTDEVELOPMENT OF TRANVERSE RANGES

  6. SUBDUCTION ZONE EARTHQUAKESLARGEST EARTHQUAKESThrust faults . Many in Alaskan Trench. Also in Middle America Trench but not so large

  7. SUBDUCTION ZONE EARTHQUAKESALASKA, MIDDLE AMERICA, CASCADIAThree major areas of subduction zone earthquakes (red) Alaska Trench, Middle America Trench, Cascadian Subduction Zone Ocean/Ocean, Ocean/Continent, Ocean/Continent collisions

  8. SUBDUCTION ZONE EARTHQUAKES1964 ALASKA EARTHQUAKEPacific plate subducted beneath North American Plate. 1000 km by 400 km slab moved 19.5 m with 3-4 min shaking. Produced uplift and subsidence Damage mostly due to tsunami Critical earthquake for under standing thrusting in subduction zones

  9. SUBDUCTION ZONE EARTHQUAKE1985 MEXICO CITY Earthquake in Middle America Trench Earthquake in middle America trench but damage mostly in Mexico City. Cocos plate moved 2.3 m at 18o over 200 by 200 km area Damage because soft lake sediments in Mexico City resonated with 1 - 2 sec frequency of surface waves.

  10. SUBDUCTION ZONE EARTHQUAKES1985 MEXICO CITY East West Accelerations at stations around Mexico City. UNAM on hard ground small accelerations. SCT on soft lake sediments lots of acceleration due to amplification effect of resonance of soft lake sediments

  11. SUBDUCTION ZONE EARTHQUAKES1985 MEXICO CITYBuilding response problems during the earthquake. 6 - 16 storey high building worst hit. Buildings of different heights banged into each other. Buildings with different heights tore apart.

  12. SUBDUCTION ZONEEARTHQUAKE GAPImportant concept in predicting where next major quake West coast of Mexico showing dates of earthquakes and the fault areas. Note that the Michoacan gap was filled by 1985 earthquake. Geurrero gap is overdue for a major movement.

  13. SUBDUCTION ZONE EARTHQUAKESPACIFIC NORTHWESTJuan de Fuca plate subducted beneath North America Volcanoes in Pacific Northwest indicate Subduction is currently active. Youthful ocean floor and strong coupling with overriding plate make this area particularly dangerous. Had 6.8 earthquake in 2001 Suggested had 9.0 earthquake in 1700

  14. SUBDUCTION ZONE EARTHQUAKESPACIFIC NORTHWEST6.8 2001020228 Nisqually earthquake

  15. SUBDUCTION ZONE EARTHQUAKEPACIFIC NORTHWEST2001 Nisqually earthquake Map of seismicity in the Pacific Northwest. Earthquake occurred deep under Tacoma Because it was so deep caused remarkably little damage at the surface even though 6.8 magnitude.

  16. SUBDUCTION ZONE EARTHQUAKESPACIFIC NORTHWEST2001 Nisqually earthquake Normal fault solution at the bend in the plate as it descends into the mantle Below the zone where the most devastating thrust earthquakes occur. Normal fault and depth are reason why damage was so small.

  17. SUBDUCTION ZONESPACIFIC NORTHWEST26 January 1700 9.0 Cascadia earthquake Annual growth rings in drowned trees along coast from BC to Oregon show all died at the same time in Jan 1700. Explanation was the ground dropped and sea water got to the roots. Had to have been a huge earthquake to cause such an extensive drop.

  18. SUBDUCTION ZONESPACIFIC NORTHWESTEvidence for a major thrust zone from margin sediments Diagram shows 1960 Chile Earth quake sequence on Cascadia subduction zone. Much seismic energy is locked up in the cold surface area of the fault. Scientists argues that if the whole fault released it could create a huge earthquake that would rotate the entire land area and create a huge tsunami. Both would kill the trees.

  19. SUBDUCTION ZONESPACIFIC NORTHWESTJapanese records show evidence of a tsunami January 26 1700 that was not from a local earthquake but probably from Pacific Northwest.

  20. SPREADING CENTER QUAKESSALTON SEA Very active, many normal fault earthquakes Map of northwestern Gulf of California and the Salton Sea. Note the two buried spreading centers between the San Andreas Fault and the northern gulf. Many earthquakes but sparsely populated and little damage. Thermal power station at Cerro Prieto.

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