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 East side Franciscan Complex rocks

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

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”

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

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

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

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

Improving The Freeways

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

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

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

Thank you for listening Any Questions?