Seismic Discrimination of Controlled Explosions and Earthquakes Near Mount St. Helens Using P/S Ratios
Abstract
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 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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 28, 2020
- Source ID
- 10.1029/2020jb020338
Entities
People
- Brandon Schmandt
- Eric Kiser
- Ruijia Wang
Organizations
- Air Force Research Laboratory
- National Science Foundation
- University of Arizona
- University of New Mexico