TY - JOUR
T1 - Seismic Discrimination of Controlled Explosions and Earthquakes Near Mount St. Helens Using P/S Ratios
AU - Wang, Ruijia
AU - Schmandt, Brandon
AU - Kiser, Eric
N1 - Funding Information:
The IRIS DMC is supported by the National Science Foundation under Cooperative Support Agreement EAR‐1851048. We thank the principal investigators and many fieldworkers involved in the iMUSH project for collecting much of the data used in the study. We thank Bill Walter, Elisa Tinti, and Colin O'Rourke for their constructive comments. Eli Baker and Keith Koper provided helpful feedback during the research. Carl Ulberg shared phase picks and a local tomography model. This research was supported by the Air Force Research Lab under contract FA9453‐19‐C‐0055.
PY - 2020/10/1
Y1 - 2020/10/1
N2 - Explosions and earthquakes are effectively discriminated by P/S amplitude ratios for moderate magnitude events (M ≥ 4) observed at regional to teleseismic distances (≥200 km). It is less clear if P/S ratios are effective explosion discriminants for lower magnitudes observed at shorter distances. We report new tests of P/S discrimination using a dense seismic array in a continental volcanic arc setting near Mount St. Helens, with 23 single-fired borehole explosions (ML 0.9–2.3) and 406 earthquakes (ML 1–3.3). The array provides up to 95 three-component broadband seismographs, and most source-receiver distances are <120 km. Additional insight is provided by ~3,000 vertical component geophone recordings of each explosion. Potential controls on local distance P/S ratios are investigated, including frequency range, distance, magnitude, source depth, number of seismographs, and site effects. A frequency band of about 10–18 Hz performs better than lower or narrower bands because explosion-induced S wave amplitudes diminish relative to P for higher frequencies. Source depth and magnitude exhibited weak influences on P/S ratios. Site responses for earthquakes and explosions are correlated with each other and with shallow crustal Vp and Vs from traveltime tomography. Overall, the results indicate high potential for local distance P/S explosion discrimination in a continental volcanic arc setting, with ≥98% true positives and ≤6.3% false positives when using the array median from ≥16 stations. Performance is reduced for smaller arrays, especially those with ≤4 stations, thereby emphasizing the importance of array data for discrimination of low magnitude explosions.
AB - Explosions and earthquakes are effectively discriminated by P/S amplitude ratios for moderate magnitude events (M ≥ 4) observed at regional to teleseismic distances (≥200 km). It is less clear if P/S ratios are effective explosion discriminants for lower magnitudes observed at shorter distances. We report new tests of P/S discrimination using a dense seismic array in a continental volcanic arc setting near Mount St. Helens, with 23 single-fired borehole explosions (ML 0.9–2.3) and 406 earthquakes (ML 1–3.3). The array provides up to 95 three-component broadband seismographs, and most source-receiver distances are <120 km. Additional insight is provided by ~3,000 vertical component geophone recordings of each explosion. Potential controls on local distance P/S ratios are investigated, including frequency range, distance, magnitude, source depth, number of seismographs, and site effects. A frequency band of about 10–18 Hz performs better than lower or narrower bands because explosion-induced S wave amplitudes diminish relative to P for higher frequencies. Source depth and magnitude exhibited weak influences on P/S ratios. Site responses for earthquakes and explosions are correlated with each other and with shallow crustal Vp and Vs from traveltime tomography. Overall, the results indicate high potential for local distance P/S explosion discrimination in a continental volcanic arc setting, with ≥98% true positives and ≤6.3% false positives when using the array median from ≥16 stations. Performance is reduced for smaller arrays, especially those with ≤4 stations, thereby emphasizing the importance of array data for discrimination of low magnitude explosions.
KW - event classification
KW - explosion monitoring
KW - network optimization
KW - upper crust structure
KW - volcanic earthquakes
UR - http://www.scopus.com/inward/record.url?scp=85093832992&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85093832992&partnerID=8YFLogxK
U2 - 10.1029/2020JB020338
DO - 10.1029/2020JB020338
M3 - Article
AN - SCOPUS:85093832992
VL - 125
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9380
IS - 10
M1 - e2020JB020338
ER -