Improved Stress Drop Estimates for M 1.5 to 4 Earthquakes in Southern California From 1996 to 2019
Improved Stress Drop Estimates for M 1.5 to 4 Earthquakes in Southern California From 1996 to 2019
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DOI：
10.1029/2022jb024243
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发表时间：
2022-06
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影响因子：
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通讯作者：
P. Shearer;R. Abercrombie;D. Trugman
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作者：
P. Shearer;R. Abercrombie;D. Trugman
我们使用P波谱分解方法估计了1996年至2019年超过7万次南加州1.5-4级地震的布伦型应力降。基于我们最近的工作，记录了绝对应力降、应力降随矩缩放、高频衰减率以及路径项和衰减项的经验校正之间难以解决的权衡，我们采用了一种新的方法，即将距离每个目标事件较短距离内的最小地震的平均拐角频率固定为恒定值。这消除了最小事件之间应力降的任何真正连贯的空间变化，但确保了在较大事件中看到的任何空间变化都是真实的，而不是不准确的路径校正的伪像。将这种方法应用于整个南加州，我们记录了与以前的工作一致的应力降的空间变化，例如索尔顿海槽中低于平均水平的应力降，以及沿许多断层和余震序列的小规模应力降变化。我们观察到3-4级地震的Brune型应力降随矩的增加而明显增加，但它们的频谱可以用高频衰减率浅于f−2的自相似模型来同样好地拟合。
We estimate Brune‐type stress drops for over 70,000 southern California M 1.5–4 earthquakes from 1996 to 2019 using a P‐wave spectral decomposition approach. Based on our recent work documenting hard‐to‐resolve trade‐offs between absolute stress drop, stress drop scaling with moment, high‐frequency falloff rate, and empirical corrections for path and attenuation terms, we adopt a new approach in which the average corner frequency of the smallest earthquakes within a short distance from each target event is fixed to a constant value. This removes any true coherent spatial variations in stress drops among the smallest events but ensures that any spatial variations seen in larger event stress drops are real and not an artifact of inaccurate path corrections. Applying this approach across southern California, we document spatial variations in stress drop that agree with previous work, such as lower‐than‐average stress drops in the Salton Trough, as well as small‐scale stress drop variations along many faults and aftershock sequences. We observe an apparent increase in Brune‐type stress drop with moment for M 3–4 earthquakes, but their spectra can be fit equally well with self‐similar models with a high‐frequency falloff rate shallower than f−2.