Analyzing Microseismicity Triggered by the DAG-2 Chemical Explosion Using Fiber Optic DAS Data
Abstract
The second chemical explosion of the Source Physics Experiment Phase 2 (Dry Alluvium Geology, or DAG) series was a 50,000 kg TNT equivalent explosion of nitromethane detonated on the Nevada National Security Site (NNSS) on 19th of December 2018. The explosion was followed by a sequence of microseisms that continued with a high rate of seismicity (>30 events per hour) in the first 24 hours (the duration of our recording). Previously, these events were located using an array of surface geophones and accelerometers. To assist the understanding of the of microseism sequence, data collected using downhole fiber optic distributed acoustic sensors (DAS) were analyzed. The two boreholes were 80 meters southwest and 80 meters east of ground zero. The fiber optic diagnostic creates the equivalent of an array of strain-rate sensors with approximately one meter spacing. The fiber optic cable extends to a depth of over 375 meters within the boreholes, with channels both above and below the depth of DAG-2. By picking the arrival times of microseisms at a range of depths, we were better able to constrain the locations of the microseisms relative to surface-only instrumentation. The fiber optic data has the greatest influence on the depths of the microseisms located in the area close to ground zero. A better understanding of the depths and time evolution of depths for the microseismic events helps to determine the most likely mechanism behind the generation of the microseismic swarm triggered by the detonation. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S11E0406R
- Keywords:
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- 7219 Seismic monitoring and test-ban treaty verification;
- SEISMOLOGY;
- 7294 Seismic instruments and networks;
- SEISMOLOGY;
- 7299 General or miscellaneous;
- SEISMOLOGY