National Seismic Hazard Mapping Project

Project Description
The National Seismic Hazard mapping Project (NSHMP) is a project
developed by the United States Geological Survey (USGS)which
involves the development of hazard maps showing the likely risk
of seismic activity throughout the United States.

The map here depict earthquake hazard by showing, by contour
values, the earthquake ground motions that have a common given
probability of being exceeded in 50 years.

The ground motions being considered at a given location are
those from all future possible earthquake magnitudes at all
possible distances from that location. The ground motion coming
from a particular magnitude and distance is assigned an annual
probability equal to the annual probability of occurrence of the
causative magnitude and distance.

The method assumes a reasonable future catalog of earthquakes,
based upon historical earthquake locations and geological
information on the recurrence rate of fault ruptures.

When all the possible earthquakes and magnitudes have been
considered, one can find a ground motion value such that the
annual rate of its being exceeded has a certain value. Hence, on
a given map, for a given probability of exceedance, PE,
locations shaken more frequently, will have larger ground
motions.

For a LARGE exceedance probability, the map will show the
relatively likely ground motions, which are LOW ground motions,
because small magnitude earthquakes are much more likely to
occur than are large magnitude earthquakes. For a SMALL
exceedance probability, the map will emphasize the effect of
less likely events: larger-magnitude and/or closer-distance
events, producing overall LARGE ground motions on the map.

The maps have this format, because they are designed to be
useful in building codes, in which we assume that, for the most
part, all buildings would be built to the same level of
safety. For other applications, maps of another format might be
more useful.

For instance, many buildings across the US are built more or
less the same, regardless of earthquake hazard. If we knew that
a particular type of building was likely to fail at a particular
ground motion level, we could make a map showing contours of the
likelihood of that ground motion value being exceeded, due to
earthquakes.

For more information,
link to http://geohazards.cr.usgs.gov/eq/