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Geology for Engineers

Geology for Engineers. The San Andreas Fault: The Geological and Civil Engineering Implications. History. The San Andreas is a collection of faults The geological history of the area is varied West side Granitic Basement, part of a volcanic arc

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Geology for Engineers

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  1. Geology for Engineers The San Andreas Fault: The Geological and Civil Engineering Implications

  2. History • The San Andreas is a collection of faults • The geological history of the area is varied • West side Granitic Basement, part of a volcanic arc • East side Franciscan Complex rocks

  3. History • East Side –Franciscan Complex • Intensely sheared and broken • Ophiolite bodies • Cold intrusive masses of Serpentinite • West Side - Salinian block • Granitic and Metamorphic rock • Theorised to have been transported from Sierra Nevada • Possibly transported 2500Km from Central America

  4. Fault Type • Strike – Slip Fault • Responsible for Transportation • San Andreas right lateral • Rupture nearly vertical • Thrust Fault • Found in LA area • One plate rises above another • When breaching the surface create “Thrust Mountains”

  5. Associated Problems • Strike – Slip Fault • Differential Movement of Surface • Sudden Slip • Earthquakes • Thrust Faults • Surface Movement • Earthquakes (underground)

  6. Earthquakes and Civil Engineering • Ground Shaking • Richter Scale • Principle Cause of earthquake damage • Ground Failure • Faults • Induced Landslides • Settlement • Liquefaction

  7. San Francisco Earthquake 1906

  8. San Francisco Earthquake 1906 • 7.8 on the Richter Scale • 300 miles of Fault Slipped up to 21ft • 80% of City destroyed • Made worse as bay area is made from soft mud, sand and gravel

  9. Ground Shaking • Predicted Cost of a San Andreas Earthquake • Engineering Solutions • Retrofitting • Dampers – Slosh Tanks, Shock Absorbers • Reinforcement – Shear Trusses • Freeways

  10. Improving The Freeways

  11. Ground Failure • Avoiding Faults • Dont Build directly on fault • Landslides • Can cause massive damage • Not a big issue on S.A. Fault • Settlement • Dependant on Subgrade • Soil Stabilisation

  12. Reducing the Effects of Liquefaction • What is Liquefaction? • Susceptible Soils • Avoidance • Compaction • Vibroflotation • Drainage • Resistant Structures • Shallow Foundations • Deep Foundations

  13. Conclusion • Existing geological profile and tendencies will remain • Movement of the slip-strike plates will continue • The build up of stresses within such faults means another big earthquake likely • Greater understanding of earthquake dynamics • Major Structures all designed to withstand major earthquakes

  14. Thank you for listening Any Questions?

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