Slopes of P‐ to S‐wave spectral ratios—A broadband regional seismic discriminant and a physical model
Slopes of P‐ to S‐wave spectral ratios—A broadband regional seismic discriminant and a physical model
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纵波与横波谱比的斜率——宽带区域地震判别式和物理模型
DOI：
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发表时间：
1995
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影响因子：
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通讯作者：
P. Goldstein
中科院分区：
文献类型：
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作者：
P. Goldstein
对核扩散的关切和就《全面禁止核试验条约》(全面禁试条约)进行的谈判强调，需要强有力的地震监测和区域区分能力，特别是在低强度情况下。标准的区域歧视技术有许多缺点。例如，他们不能总是区分浅层、低震级地震或与采矿有关的事件。我指出，P波与S波谱比的斜率可以用来区分浅层和正常深度的地震和爆炸，并可能用来区分爆炸和与采矿有关的岩爆或坍塌事件。P波至S波斜率和常规高频P波至S波谱振幅比联合使用比单独使用更能区分地震。内华达试验场爆炸和地震的Pn谱和Lg谱的比较表明，这种方法区分集中爆炸和地震以及其他浅层地震事件(如矿山坍塌)，是因为爆炸产生的S波在高频下衰减得比地震产生的S波快。一维反射率合成地震记录的频谱表明，爆炸产生的P波到S波转换相在近地表的频率相关衰减可能是造成Lg(S波)谱衰减差异的原因。这些模拟还表明，地震P波与S波谱比的绝对幅度对机制和深度非常敏感，这可能有助于解释常规方法的不同表现。
Concerns about nuclear proliferation and negotiations toward a Comprehensive Test Ban Treaty (CTBT) emphasize the need for robust seismic monitoring and regional discrimination capabilities, especially at low magnitudes. Standard regional discrimination techniques have many shortcomings. For example, they cannot always discriminate shallow, low-magnitude earthquakes or mining-related events. I show that slopes of P- to S-wave spectral ratios can be used to discriminate shallow- and normal-depth earthquakes from explosions and possibly to discriminate explosions from mining-related rockburst or collapse events. P- to S-wave slopes and conventional, high-frequency P- to S-wave spectral amplitude ratios discriminate even better in combination than alone. A comparison of Pn and Lg spectra from Nevada Test Site (NTS) explosions and earthquakes shows that this method discriminates concentrated explosions from earthquakes and other shallow seismic events such as mine collapses because S waves from explosions decay more rapidly at high frequencies than do S waves from earthquakes. Spectra of one-dimensional reflectivity synthetic seismograms show that frequency-dependent attenuation of explosion-generated P- to S-wave converted phases, in the near-surface layers, may be responsible for the differences in Lg (S-wave) spectral falloff. These simulations also show that absolute amplitudes of earthquake P- to S-wave spectral ratios are very sensitive to mechanism and depth, which may help explain the variable performance of conventional methods.