Microseismicity Associated With the DAG-2 Chemical Explosion

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

The Dry Alluvium Geology (DAG) 2 chemical explosion conducted at the Nevada National Security Site (NNSS) in December, 2018, initiated a robust sequence of microseismic events immediately following the explosion. DAG-2 is a 50,000 kg TNT-equivalent charge of nitromethane detonated at 300 meters below ground surface in the alluvium of Yucca Flat, Nevada, on the NNSS. Within seconds of the detonation, a microseismic swarm, detectible on a seismic array to over 1500 m distance from ground zero, was initiated. At its peak, the swarm comprised over 100 events per minute. A high rate of seismicity (> 30 events per hour) continued for over 24 hours. We present data and analysis of this swarm in terms of event decay rate, moment release, and hypocenter distribution. Events were picked via template matching on a 500-channel array of surface geophones and accelerometers and two downhole fiber optic distributed acoustic sensing (DAS) cables deployed 80 m from ground zero. We also explore time-reversal location methods with imaging conditions adapted to microseismicity to determine hypocenter locations for comparison purposes. Early indications are that these events are associated with collapse of the stemming material above the detonation into the post-explosion cavity. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Presenting Author: Austin A. Holland

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