Earthquake prediction and structure safety

Predicting earthquakes has been very controversial subject. Seismologists can only predict that movement is “possible” along a certain fault line or it is imminent. The two aspects of the prediction – where and when – are not easy to determine. So typically, what seismologists give, are “forecasts” – not predictions. They give an estimated location, and time of an earthquake of possible magnitude.

So when structures are being built, one needs to study the “seismic hazards” that the structure will likely face. The seismic hazards that can affect a structure due to a nearby earthquake are classified as primary and secondary. Primary hazards includes ground rupture, while secondary hazards includes ground shaking, ground lurching, liquefaction, etc.

Ground rupture occurs at the surface of active faults. Since the location of a fault, deep within the earth may not be known accurately or since there may be several small faults at a given location, “fault hazard zones” are demarcated on the surface by geologists and seismologists. Any construction should be avoided within these zones.

Ground shaking occurs in all earthquake prone areas, and to mitigate the effects of shaking, all structures must be built and designed as per local building codes and using sound engineering judgment.

Since it is not practical and uneconomical to build structures that resist maximum possible earthquakes with minimum damage, the building codes typically follow a few principles. The Uniform Building Code (UBC) lays down the following requirements:

• The structures should be able to resist minor earthquakes without damage
• The structures should be able to resist moderate earthquakes without structural damage but with some nonstructural damage
• The structures should be able to resist major earthquakes without collapse but with some structural as well as nonstructural damage.

Although this does not guarantee that severe structural damage will not occur, at least we can expect that the structure will not collapse.

Here are some interesting sites that talk about earthquake prediction:

• Quake prediction on west coast of USA
• Satellites and Earthquake Prediction
• Earthquake Prediction Research Center
• Earthquake Hazards Program at USGS

Copyright Kshitija Nadgouda.