High-order azimuth coherent imaging for microseismic location

The cross-correlation-based methods, widely used for microseismic monitoring, utilize cross-correlation to extract time differences of signals within station pairs, and subsequently use these time differences for back-projection and localization without the need for triggering moment scanning. The selection of imaging conditions, applied to the spatial projection of all cross-correlation records, determines the noise resistance and resolution of such methods. To fully exploit the azimuthal properties of station pairs for constraining the source imaging, we propose a high-order azimuth coherent imaging condition, which involves the following steps: (i) choosing station pairs that meet specific inter-station distance criteria; (ii) combining station pairs into dual-station pairs that satisfy a certain inter-station pair angle criterion; (iii) further combining station combinations pairwise to form the final set of station pairs; (iv) multiplying the projection results of station pairs within each combination from the third step; and (v) summing the results of all combinations. This method effectively suppresses the hyperboloid in the spatial projection of a single station, enhances the coherence of seismic source imaging, and maintains noise resistance. Compared to the conventional imaging conditions, the method proposed has demonstrated superior resolution and robustness in both theoretical analysis and practical testing.