Earthquake Effects On Tall Buildings

Types of Earthquake Faults

  • Only convergent and transform boundaries tend to cause large earthquakes.
  • Divergent boundaries do cause earthquakes as well, but these tend cause much less  damage.
  • Convergent boundaries are mostly found just offshore of many continents, where an oceanic plate subducts beneath a continental plate
  • Most of the world’s population lives within 50 miles of an ocean, so typically these earthquakes cause the most casualties and destruction.
  • Convergent boundaries can also be on continents, where two plates of continental crust are colliding, such as the boundary that created the Himalaya Mountains.

1985 MEXICO EARTHQUAKE

  • EPICENTER LOCATED 240 KM FROM MEXICO CITY
  • 400 BUILDINGS COLLAPSED IN  OLD LAKE BED ZONE OF MEXICO CITY
  • SOIL-STRUCTURE RESONANCE IN OLD LAKE BED ZONE WAS  A  MAJOR  FACTOR

Resonance

  • Resonance = frequency content of the ground motion is close to building’s natural frequency

–tends to increase or amplify building response

–building suffers the greatest damage from ground motion at a frequency close or equal to its own natural frequency

  • Example: Mexico City earthquake of September 19, 1985

–majority of buildings that collapsed were around 20 stories tall

–natural period of around 2.0 seconds

–other buildings, of different heights and different natural frequencies, were undamaged even though located right next to damaged 20 story buildings

 

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