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Analysis of the Source Physics Experiment, Dry Alluvium Geology Ball Drop Sources

Session: Explosion Seismology Applications and Advances [Poster]

Type: Poster

Date: 4/19/2021

Presentation Time: 11:30 AM Pacific

Description: 

The Source Physics Experiment (SPE) is a multiphase experiment to better understand explosion source physics and thereby improve explosion monitoring. The second phase of the SPE consisted of four chemical explosions in alluvium referred to as the Dry Alluvium Geology (DAG) series of chemical explosions. The second of the DAG chemical explosions (DAG-2) resulted in an energy release of 51 TNT-equivalent tonnes and created a large cavity and damage region around the working point resulting in an energetic aftershock sequence.

One potential source of explosion aftershocks is rubble collapsing into the borehole and cavity. In order to better identify which events in the aftershock sequence could be due to such a mechanism an attempt was made to replicate their signals. About 3 months after the DAG-2 detonation two ball weights were dropped from a height of 150.9 m above the bottom of the borehole. The bottom of the borehole at this time was about 150 m above the DAG-2 working point to make a floor for the DAG-3 canister. The first ball drop was a 14.27 kg concrete-filled basketball and the second was a 7.24 kg bowlingball.

The ball drop signals were used as templates to search for similar events in the DAG-2 aftershock sequence recorded on the local array of stations distributed near the DAG borehole. The bowlingball template correlated with zero events and the basketball correlated with four events in a 75 day period beginning with the DAG-2 detonation. During the same period Ichinose et al. (2021) report more than a thousand events. A synthetic sensitivity study showed that the high-frequency template detections were only sensitive to a small region near where the balls landed at 150.9 m that did not extend to the actual location of the DAG-2 cavity near a depth of 300 m. Therefore, it appears that the four detected events were probably from debris falling in the borehole and striking the floor near 150.9 m depth just as the ball drops had done and the majority of aftershocks have a different source type and location.

Prepared by LLNL under Contract DE-AC52-07NA27344.

Presenting Author: Sean R. Ford

Student Presenter: No

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