Using network data, the Bureau's Earthquake Studies Office has compiled a catalog of over 12,000 earthquakes throughout Montana and adjoining parts of Idaho, Wyoming, and Canada since 1982. Along with the original readings used to locate the earthquakes, these data form a unique and valuable resource for studying the seismicity in our region and for assessing seismic hazards, particularly those associated with blind faults. However, before these data can be used to full potential, biases in the hypocenter locations must first be identified and then removed. Larger octagons are historic earthquake epicenters with magnitudes of 5.5 or larger from National Oceanic and Atmospheric Admin- istration. Triangles indicate Montana seismograph network station locations.
Squares show city and town locations.
Bold line segments show active fault locations. Slightly bolder segments are faults that have produced major earthquakes during the past 12,000 years. The process of locating earthquake hypocenters has advanced considerably from the old days of drawing intersecting arcs on a globe or wall map to find an epicenter. Today, the task of locating earthquakes relies on computers with sophisticated programs. A model describing the velocities of seismic waves between an earthquake hypocenter and the seismic recording stations also must be known.