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Loma Prieta Earthquake Mourad Amouri Nicolas Rodriguez.

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1 Loma Prieta Earthquake Mourad Amouri Nicolas Rodriguez

2 Date: October 18, 1989 at 00:04 UTC (October 17, 1989 at 05:04 PM local time) Location: Depth: km Magnitude: 7.1 Deaths: 63 Injuries: 3,757 Property Damage: $ 5,900,000,000. At the time, this was the most costly natural disaster in the United States. Earthquake Data

3 Length: 1280 km Depth: 17 km Width: from 50 m to 600 m Type of displacement: right-lateral strike-slip Average strike-slip displacement : 1.6m Average reverse-slip displacement: 1.2m San Andreas’ fault

4 Causes of the damage Ground Shaking  The intensity of ground shaking at a specific location is a function of the distance from the earthquake epicenter and the way in which seismic waves propagate through different kinds of subsurface materials. Landslides  Seismic events can both initiate land sliding and reactivate older massive landslides. Liquefaction  Liquefaction can occur when saturated, cohesion less soil experiences a cyclic shear stress.

5 Liquefaction Before the sand regains stability the ground may deform either  Moderately (ground cracking)  Catastrophically (ground flow) Many existing buildings throughout the San Francisco Bay are located on poorly consolidated deposits or man-made fill potentially subject to liquefaction during earthquakes. The areas affected by liquefaction have a high water table and are underlain by fine-grained sand. Example of areas affected : Port of Oakland, Marina district

6 Liquefaction Liquefaction-induced damage to taxiway pavement. Large sand boil near north end of main runway at Oakland International Airport

7 Mitigation processes Ground shaking  Potential damage from future ground shaking can only be mitigated by tailoring structural designs and land use to the geologic setting. Landslides  Avoid building in areas of slope instability.  Difficult to predict where new or reactivated land sliding may occur during earthquakes. Liquefaction  Structures built on areas that liquefy may collapse as a result of ground failure and movement.  Avoid building in areas likely to liquefy during seismic shaking.

8 Case study: Cypress viaduct Two main causes for the collapse of the Cypress Viaduct: Geotechnical characteristics of the area: structure built on soft “mud” which had increase by up to five the amplitude of vibration. Design mistake:  inadequate transverse reinforcement in the columns;  ineffective bent cap and pin connection design;  improper compensation for the weak soil conditions.

9 Case study: Cypress viaduct The Cypress viaduct collapsed in the 1989 Loma Prieta Earthquake. Reconstruction took place on an entirely new alignment. Lightweight cellular concrete. In some locations the roadway section is below the water table Negative surcharge to the San Francisco Bay Mud material

10 Conclusion This earthquakes was not the “Big One” feared by all the Californians Still 62% to have a a M>=6.7 earthquake during the next 30 years New building code was created in 2000 using a set of State-wide shaking-hazard maps based on current knowledge of more than 200 active faults and of the historical earthquake record. These maps depict geographic variations in the likely maximum severity of shaking to be experienced within a 50-year period.


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