![coda define coda define](https://upload.wikimedia.org/wikipedia/commons/c/c1/Music-coda.png)
The first explosion, SPE-1, was equivalent to 87.9 kilograms of TNT. The researchers used coda wave interferometry to determine the known relative location of two chemical explosions that took place during Phase I of the SPE.
![coda define coda define](https://seeseekey.net/wp-content/uploads/2012/06/coda.png)
The SPE conducts chemical explosions to better understand the seismic waves they produce and to refine explosion detection techniques, using the analyses to improve monitoring of global nuclear explosions. In the new study, Ford and Walter used data from the SPE, an ongoing multi-institutional project involving Lawrence Livermore, Los Alamos and Sandia National Laboratories at the former Nevada nuclear test site. Any changes in the scattering structure - from rocks pushed or crushed by an explosion, for example - "will show up in how these later arriving waves have bounced around in that medium over a greater duration," Ford explained. Unlike the direct and strong P- and S-seismic waves produced by an earthquake or explosion event, coda waves arrive later and are more sensitive to scattering by the rock that they pass through. "Based on the size and frequency scaling that we were able to employ in the paper and successes at SPE," said Ford, "a conclusion point is that this technique could be used for larger explosions at larger separations recorded at more distant stations" such as those used to monitor North Korean testing. The findings suggest the technique could be used to improve the estimates of the relative locations of larger explosions, such as the series of announced nuclear tests conducted by the Democratic People's Republic of Korea over the past two decades. Lawrence Livermore National Laboratory researchers Sean Ford and Bill Walter report that coda wave interferometry can also put a limit on the extent of damage caused by an explosion.
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The technique, called coda wave interferometry, was tested on explosions conducted as part of the Source Physics Experiment (SPE).