81-1 Drilling a Fault is No Bore: Preliminary Analysis and Lessons Learned from Drilling a 2-Kilometer Deep Corehole in the Rock Valley Fault Zone, Southern Nevada

Session: Investigating Earth’s History With Continental Scientific Drilling

Presenting Author:

Matthew Dietel

Authors:

Dietel, Matthew¹, Freimuth, Clayton², Aittama, Morgan³, Downs, Nicholas⁴, Montano, Hali⁵, Larotonda, Jennifer⁶, Smith, Devon⁷, Miller, Andrew⁸, Pine, Jesse⁹, Wilson, Jennifer¹⁰, Bonner, Jesse¹¹, Snelson, Catherine M.¹², Walter, William R.¹³, Alger, Ethan¹⁴, Abbott, Robert E.¹⁵

(1) Nevada National Security Sites, Mercury, USA, (2) Nevada National Security Sites, Mercury, USA, (3) Nevada National Security Sites, Mercury, USA, (4) Nevada National Security Sites, Mercury, USA, (5) Nevada National Security Sites, Mercury, USA, (6) Nevada National Security Sites, Mercury, USA, (7) Nevada National Security Sites, Mercury, USA, (8) Nevada National Security Sites, Mercury, USA, (9) Nevada National Security Sites, Mercury, USA, (10) Sandia National Laboratories, Albuquerque, USA, (11) Lawrence Livermore National Laboratory, Livermore, USA, (12) Los Alamos National Laboratory, EES-17, Los Alamos, USA, (13) Lawrence Livermore National Laboratory, Livermore, USA, (14) Lawrence Livermore National Laboratory, Livermore, USA, (15) Sandia National Laboratories, Albuquerque, USA,

Abstract:

The Rock Valley Fault Zone (RVFZ), located in southern Nevada, is an active, transtensional fault zone that developed in the late Paleogene and produced a sequence of shallow earthquakes in 1993. Understanding the RVFZ and Rock Valley stratigraphy is important because this section records syntectonic deposition and deformation associated with the onset of regional Basin and Range extension and may inform the Cenozoic tectonic evolution of southern Nevada. The Rock Valley Direct Comparison (RV/DC) project is investigating signature differences between subsurface explosions and earthquakes in this area. Conducting these dynamic experiments in a tectonically active region requires a comprehensive subsurface geology model of the region. Research conducted as part of the project is providing critical ground-truth constraints for the model. It will also improve our understanding of fault development and basin evolution in transtensional systems, offering valuable insight for both geologic hazard assessment and regional tectonic models. The RV/DC project recently drilled a 2-kilometer deep vertical corehole, named UE-27a, targeted near the hypocenter zone of the 1993 earthquake sequence. The uniquely shallow nature of these earthquakes provided a novel opportunity to drill near a recent fault. Drilling UE-27a produced PQ-sized core (85-mm diameter) from 0 to 1274 meters and HQ-sized core (64 mm diameter) from 1274 to the total depth of 2090 meters. The corehole was completed ahead of schedule, with our scientific goals of 98% core recovery and multiple datasets from downhole geophysical surveys accomplished. We present how we navigated challenging project conditions during the drilling program. We also show preliminary scientific data acquired from core and downhole geophysical surveys, which indicate a more developed Cenozoic basin than predicted. At least two distinct units with varied depositional environments are interpreted in the Cenozoic section of the core, which lies disconformably on Paleozoic carbonate rocks at 1183-meter depth. Subsequent detailed logging and interpretation of these data aid geologic modeling required for the RV/DC project, provide important context for basin evolution at Rock Valley, and give insight into a complex history of strain within the RVFZ. This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy and the National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation. DOE/NV/03624--2227

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5343

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