Intraplate Seasonal Seismicity in the Northern Rocky Mountains of Montana and Idaho

Hydrologic processes have been shown to influence seismic productivity in many regions around the world, especially on active plate boundaries. To examine the influence of hydrologic loading cycles on seismicity in intraplate regions, we investigate temporal patterns of seismic productivity in the northern Rocky Mountains of Montana and Idaho. Seasonal variations in seismicity are present, with enhanced productivity in December and January, and reduced productivity in June and July. Using Snowpack Telemetry and GPS data, we find that seismicity is temporally correlated with the highest hydrologic loading rates rather than peak load, consistent with rate and state models of fault behavior for faults in critically stressed domains. However, we cannot distinguish between high hydrologic stress rates and pore pressure increases at seismogenic depths lagging ∼6 months after peak snowmelt.