Map 8-1 Purcell Trench
Quaternary Fault and Fold Database for the United States
Last modified November 17, 2004
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 http://eqint.cr.usgs.gov/eq/html/lookup-2002-interp.html
or at the Earthquake Hazards Program website http://eqhazmaps.usgs.gov/faq/psha02.html
(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
The input zip-code is 83805. Bonners Ferry, Idaho
ZIP CODE 83805
LOCATION 48.6977 Lat. -116.3169 Long.
DISTANCE TO NEAREST GRID POINT 1.2672 kms
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
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
of Exceedance for Boundary County
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.
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 (http://eqhazmaps.usgs.gov/ 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
8-5 Earthquake Risk for
Seismicity of Idaho, 1990 - 2001
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.|