Map 8-1   Purcell Trench

Map 8-2

Quaternary Fault and Fold Database for the United States




Last modified November 17, 2004  


The National Seismic Hazard Mapping Project produces maps showing national earthquake hazards expressed as probabilistic ground motions. The probabilistic ground motion value for any desired site in the United States can be looked up by latitude and longitude, or by zip code at or at the Earthquake Hazards Program website (as seen in Table 8-1, below).  This site also provides definitions of Peak Ground Acceleration (PGA) and 0.2 and 1.0 sec Spectral Acceleration (SA). 

Table 8-1.  Probabilistic Ground Motions for Bonners Ferry

USGS, Earthquake Hazards Program - National Seismic Hazard Mapping
(Link to USGS home page.)

   The input zip-code is 83805.  Bonners Ferry, Idaho

   ZIP CODE                        83805

   LOCATION                        48.6977 Lat. -116.3169 Long.


   NEAREST GRID POINT              48.7 Lat. -116.3 Long.

   Probabilistic ground motion values, in %g, at the Nearest Grid point are:

               10%PE in 50 yr   5%PE in 50 yr   2%PE in 50 yr

      PGA        6.330679         8.697392       13.437380

   0.2 sec SA   13.833410        18.982620       30.260580

   0.3 sec SA   12.398080        17.682159       27.169500

   1.0 sec SA    4.224729         6.044158        9.142096

   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Map 8-3  

Probability of Exceedance for Boundary County

See for a definition of Probability of Exceedance (PE).  PE values are given for firm rock and may change over short distances because of local soil conditions.




Map 8-4

This seismic hazard map for Idaho shows earthquake ground motions that have a specified probability of being exceeded in 50 years. These ground motion values are used for reference in construction design for earthquake resistance. The ground motion values can also be used to assess relative hazard between sites, when making economic and safety decisions ( accessed 1/18/05).

LEPC Relative Risk Rating  The LEPC gave earthquake was given a relative risk hazard rating of 8.  The LEPC determined that over 75 percent of the developed area of the county would be impacted should an earthquake occur.  Although the probability of earthquake occurrence is unknown, the LEPC consensus, based on available information, is that it would be rare to have an earthquake that would have substantial negative impact to property, environment, health and safety of people, or the economy in Boundary County.  Map 8-5 below shows the risk of earthquake in Boundary County to be moderate.



Map 8-5    Earthquake Risk for Idaho


Map 8-6


Seismicity of Idaho, 1990 - 2001


Map 8-7   Locations of Earthquakes in Boundary County

As Documented by Idaho Bureau of Homeland Security


Three significant earthquakes have been documented by the Idaho Bureau of Homeland Security since 1952.   No damage was recorded for any of these events.  On September 9, 1952, a 4.0 magnitude earthquake occurred near the City of Bonners Ferry.  On July 30, 1984 there was a 4.1 magnitude north of the city of Moyie Springs.   On November 27, 1984,  a 3.2 magnitude quake occurred approximately ten miles to the north of Bonners Ferry.