Reliable detection of weak signals is potentially a fundamental limitation for microseismic event detection and location, especially for sensors in the near-surface region, where large source distances and high noise levels affect the signal-to-noise ratio (SNR). Previously, a nonlinear stacking method was introduced that could increase the SNR for weak signals and included methods that are insensitive to changes in signal polarity. This paper introduces nonlinear filtering methods that are a generalization of the nonlinear stacking method where the stacking operation is replaced by a filtering operation. This method keeps the SNR and polarity benefits of the stacking methods, but we can now choose to modify the pass and reject bands. For instance, we can improve the SNR for weak signals, with polarity changes, and allow additional signal misalignment criteria to be included in the passband. We will show synthetic-signal and real-signal examples where the new method has clear benefits compared to conventional stacking or other nonlinear stacking methods.


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