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 (M_L 0.9–2.3) and 406 earthquakes (M_L 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 V_p and V_s 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.

中文翻译：

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利用P / S比值对圣海伦斯山附近的受控爆炸和地震进行地震识别

在区域到远震距离（≥200 km）观察到中等强度事件（M≥4）的P / S振幅比可以有效地区分爆炸和地震。对于较短距离下观察到的较低量级，P / S比是否是有效的爆炸判别还不太清楚。我们提出的新的测试P /小号使用近圣海伦斯山大陆火山弧设置密集的地震台阵的歧视，有23一次烧成的钻孔爆炸（M_大号0.9-2.3）和406级地震（M_大号1–3.3）。该阵列最多可提供95个三分量宽带地震仪，并且大多数源接收器距离均小于120 km。每次爆炸的约3,000个垂直分量地震检波器记录提供了更多信息。研究了对本地距离P / S比的潜在控制，包括频率范围，距离，幅度，震源深度，地震仪数量和场地效应。大约10–18 Hz的频带比较低或较窄的频带有更好的表现，因为对于较高的频率，爆炸引起的S波振幅相对于P会减小。震源深度和震级对P / S的影响很小比率。地震和爆炸的现场响应相互关联，并且与行进时层析成像的浅层地壳V _p和V _s相关。总体而言，结果表明，在大陆火山弧环境中，局部距离P / S爆炸识别的可能性很高，当使用来自≥16个站点的阵列中值时，真实正值≥98％，错误正值≤6.3％。对于较小的阵列，尤其是那些≤4个站点的阵列，性能会降低，从而强调了阵列数据对于区分低强度爆炸的重要性。