Idaho Earthquakes of 1905, 1913, and 1916: Intensity, Location, and Magnitude Inferred from Newspaper Accounts

The purpose of this project is to better understand the epicentral location, magnitude, and effects of three southern Idaho earthquakes which occurred in 1905, 1913, and 1916. The three earthquakes are of considerable interest to seismologists owing to their reported proximity to large power dams, multistory buildings, and the nuclear facilities at Idaho National Engineering Laboratory (INEL) in south-central Idaho. structures were built in previous years without assessment of the potential for earthquake damage. Therefore, an understanding of these three earthquakes is important for future development, and for the reevaluation of potential earthquake hazard and adequacy of building codes. The 1905 earthquake is reported to have occurred near the town of Shoshone, on the Snake River Plain. It caused significant damage in Shoshone and was felt throughout the southern half of Idaho and into parts of Utah. This epicentral location has caused considerable interest due to the relative aseismicity of the Snake River Plain (Figure 1) (Pelton, et. al., 1990). Some facilities at INEL, also located on the plain, were built with design criteria for areas distant from a zone of active seismicity. If the earthquake did occur at Shoshone, it could indicate that earthquakes of sufficient magnitude to cause damage have historically occurred on the plain, and the seismic designs at INEL may need to be reviewed. The 1913 earthquake was reported to have occurred in the Hells Canyon area. This was the strongest shock known to have occurred in this region. An important observation regarding this earthquake is its long duration at Landore, Idaho reported to be over one minute. Increased duration is known to increase the destructive capability for even moderately strong earthquakes (Page and others, 1975). Although this earthquake occurred in an area that is still remote and sparsely populated, it is of considerable interest due to the near vicinity of large power dams on the Snake River. The 1916 earthquake was reported to have occurred near Boise, affecting an area of 50,000 square miles (Woodward-Lundgren and Assoc., 1972). Mann (1989) believes the epicenter was actually to the northwest of Boise near Brownlee Dam in Hell\u27s Canyon. If the earthquake did occur in the vicinity of a large dam, the seismic risk and adequacy of design may need to be evaluated. However, if the event occurred near Boise, existing buildings and building codes may need to be reevaluated