Regional Seismic Network Monitoring in the Eastern Intermountain West

The Intermountain West (IMW) region is bounded by the Sierra Nevada Mountains to the west and the Great Plains to the east. Tectonically, the region is dominated by active extension and has moderate to high seismic hazard. Both paleoseismic and historical records include M> 7 surface-rupturing earthquakes. The region is also the location of frequent moderate-size (M 5-6) earthquakes. In this article, we focus on the eastern IMW and its six regional seismic networks. We document recent and historical seismicity, describe the evolution of the regional networks, and clarify the rationale for sustained and improved seismic monitoring. Although absolute population is relatively low compared with other parts of the country, the IMW is experiencing rapid growth. Beyond population, there is significant seismic risk posed to major transportation and energy corridors, nuclear generation and storage facilities, dams, national laboratories, military bases, and other critical facilities. Despite the relatively high seismic hazard and increasing risk, seismic monitoring varies from excellent to skeletal, with some seismically active regions having minimal seismographic coverage. Clear monitoring needs for the IMW include increased station density, replacement of outdated seismic equipment, and more stable funding.