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WHAT DETERMINES DESTRUCTION?

WHAT DETERMINES DESTRUCTION?

BUILDING MATERIALS

Building material choices can influence the amount of damage caused by earthquake shaking. The flexibility of building materials relates to their resistance to damage by earthquake waves. Unreinforced Masonry (URM) is the most devastated by ground shaking. Wood framing held together with nails which can bend and flex with wave passage are more likely to survive earthquakes. Steel also can deform elastically before brittle failure. The Salt Lake City campaign “Fix the Bricks” has useful information on URMs and earthquake safety.

SHAKING INTENSITY AND DURATION

Greater shaking and duration of shaking will cause more destruction than less shaking and shorter shaking.

RESONANCE

Resonance is when the frequency of seismic energy matches a building’s natural frequency of shaking, determined by properties of the building, and intensifies the amplitude of shaking. This famously happened in the 1985 Mexico City Earthquake, where buildings of heights between 6 and 15 stories were especially vulnerable to earthquake damage. Skyscrapers designed with earthquake resilience have dampers, and base isolation features to reduce resonance.

Changes in the structural integrity of a structure could alter its resonance. Conversely, changes in measured resonance can indicate potential changes in structural integrity.

EARTHQUAKE RECURRENCE

Geologists dig earthquake trenches across some faults to measure ground deformation and estimate the frequency of occurrence of past earthquakes. Trenches are effective for faults with relatively long recurrence intervals (100s to 10,000s of years), which is the period between significant earthquakes. In areas with more frequent earthquakes and more measured earthquake data, trenches are less necessary. A long hiatus in earthquake activity could indicate the buildup of stress on a specific segment of a fault with strain held in place by friction, which would indicate a higher probability of an earthquake along that segment. This hiatus of seismic activity along a length of a fault (i.e., a fault that is locked and not having any earthquakes) is known as a seismic gap.

LICENSE

 

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Introduction to Physical Geography by R. Adam Dastrup is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Kategoria: Moje artykuły | Dodał: kolo (2019-04-04)
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