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Is Seismic Hazard the Same as Seismic Risk?

Posted by on Mar 24, 2015 in Geology | 0 comments

Seismic means “of or relating to earthquakes or other vibrations of the earth and its crust.” This can be of natural i.e. earthquakes, or manmade i.e. dynamite explosion, origin. A seismic hazard, therefore, is a phenomenon such as an earthquake.

However, this is distinct from seismic risk, which is a phenomena that has the potential to cause harm from exposure. An earthquake out in the middle of an uninhabited island is a hazard; there is no risk involved because no loss or damage is done to people. If the island was inhabited, the people would be vulnerable to loss and damage, and this constitutes a risk.

The factors considered in calculating a seismic hazard is different from that of a seismic risk. Determining a seismic hazard uses three geologic measurements: physical, spatial, and temporal. The level of severity of a potential quake, which recurs over a certain period in a specific area, determines if that area is a seismic hazard zone. To determine risk is more complicated because estimating vulnerability depends on many subjective factors.

There are several models used to estimate seismic risk, which can be expressed as seismic hazard x vulnerability One of the most commonly used is the Poisson model, but it is not any more accurate than other models. Calculating seismic risk using the Poisson model will yield different results from using as time-predictable or Brownian passage time models.

Perhaps because seismic risk is more volatile than seismic hazard, the California Geological Survey has chosen to load its dices, so to speak, by requiring cities and counties to contribute data to the Seismic Hazard Zonation Program. This will be included in the Seismic Hazard Maps for each area. Being on a designated Seismic Hazard Zone does not necessarily mean that you are in a zone of high seismic risk. However, it would be prudent to know, as forewarned is forearmed.

If you are selling a home, you have to access this data for the standardized National Hazard Disclosure (NHD) statement you will give to potential buyers. You can find out more easily if your property is in a seismic hazard zone by consulting with an excellent natural hazard disclosure company in your area.

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