Seismic Discrimination of Controlled Explosions and Earthquakes Near Mount St. Helens Using P/S Ratios

Ruijia Wang, Brandon Schmandt, Eric Kiser

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


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.

Original languageEnglish (US)
Article numbere2020JB020338
JournalJournal of Geophysical Research: Solid Earth
Issue number10
StatePublished - Oct 1 2020


  • event classification
  • explosion monitoring
  • network optimization
  • upper crust structure
  • volcanic earthquakes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


Dive into the research topics of 'Seismic Discrimination of Controlled Explosions and Earthquakes Near Mount St. Helens Using P/S Ratios'. Together they form a unique fingerprint.

Cite this