Discrimination of Small Earthquakes and Buried Single-Fired Chemical Explosions at Local Distances (<150 km) in the Western United States from Comparison of Local Magnitude (M_L) and Coda Duration Magnitude (M_C)

Journal Article · Tue Oct 13 00:00:00 EDT 2020 · Bulletin of the Seismological Society of America

DOI:https://doi.org/10.1785/0120200188· OSTI ID:1787197

Koper, Keith D. ^[1]; Holt, Monique M. ^[1]; Voyles, Jonathan R. ^[1]; Burlacu, Relu ^[1]; Pyle, Moira L. ^[2]; Wang, Ruijia ^[3]; Schmandt, Brandon ^[3]

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1. Univ. of Utah, Salt Lake City, UT (United States)
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
3. Univ. of New Mexico, Albuquerque, NM (United States)

Seismologists distinguish underground nuclear explosions from more commonly occurring earthquakes using moment tensor inversion, high-frequency P/S amplitude ratios, m_b:M_s comparisons, and P–pP differential travel times. These methods are generally successful for large seismic events (M >3-4) well recorded at regional-to-teleseismic distances (>150 km); however, it is unclear whether they can be modified to work for small events (M <3) well recorded only at local distances (<150 km). Here, we evaluate a recently proposed, local-distance seismic source discriminant—the difference between local magnitude (M_L) and coda duration magnitude (M_C)—using seismograms of earthquakes and buried, single-fired chemical explosions recorded in three regions of the western United States. The quantity M_L–M_C was previously found to be sensitive to source depth, effectively discriminating mine blasts, induced earthquakes, and very shallow tectonic earthquakes from deeper crustal earthquakes. In this study, we report the first evaluation of M_L–M_C as a depth discriminant using data from buried, single-fired explosions that, unlike the seismic sources studied earlier, are good analogs for underground nuclear explosions. We find that even when using generic, uncalibrated methods of assigning magnitudes, M_L–M_C separates single-fired explosions and earthquakes. The area under the receiver operating characteristic curve is 0.92 for 19 explosions and 14 earthquakes in Washington, 0.90 for 22 explosions and 90 earthquakes in Wyoming, and 0.99 for three explosions and 149 earthquakes in Nevada. Finally, M_L:M_C comparisons have the potential to enhance discrimination based on high-frequency P/S amplitudes ratios—which perform less well at local than regional distances—because the two metrics have complementary sensitivities.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-06NA25946; AC52-07NA27344
• OSTI ID: 1787197
• Report Number(s): LLNL-JRNL--809008; 1015049
• Journal Information: Bulletin of the Seismological Society of America, Journal Name: Bulletin of the Seismological Society of America Journal Issue: 1 Vol. 111; ISSN 0037-1106
• Publisher: Seismological Society of America
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
geosciences