Friday seminars of Institute of Earth Sciences, February 6th 2026 - Colin Nathanael Pennington (Research Staff Scientist, Lawrence Livermore National Laboratory)

Abstract:

Distinguishing earthquakes from underground explosions is a long-standing challenge, particularly for shallow events where common screening metrics can be ambiguous. The Rock Valley Direct Comparison (RV/DC) experiment isolates source-related seismic signatures by directly comparing an earthquake and a chemical explosion at the same depth and in the same geologic setting, minimizing uncertainties from depth, path, site effects, and material properties. Rock Valley at the Nevada National Security Site provides a unique natural laboratory due to a well-documented sequence of unusually shallow earthquakes (~1–3.5 km depth) and ongoing microseismicity within an active fault zone. A 2-km-deep continuously cored borehole was drilled through the Rock Valley Fault Zone to characterize subsurface structure and physical properties to better characterize the site for future drilling. Core observations, geophysical logs, and distributed fiber-optic sensing reveal complex stratigraphy, multiple fault zones, fractured carbonates, and evidence for active fluid flow. Borehole geophones and fiber-optic arrays now enable high-resolution monitoring of seismicity and fault-zone processes. These data refine geologic and velocity models and guide forthcoming controlled explosion experiments, improving physical understanding of shallow seismic sources.

All are welcome.