Decomposing Earthquake Moment Tensors Using P‐Wave First Motion: Insights Into Global Events With Significant Non‐Double‐Couple Components

The decomposition of earthquake moment tensors into isotropic and deviatoric components is standard in seismology. The deviatoric part is further separated into double‐couple (DC) and non‐double‐couple (NDC) components, with NDC providing insights into source complexity. However, existing methods often yield inconsistent results with different physical interpretation. We propose a novel decomposition method that models an earthquake as two DC subevents, in which the first is determined by P‐wave first‐motion data and the second is derived analytically via moment conservation. This method is simple, efficient, and physically interpretable. We evaluate its stability and apply it to eight global M w ≥ 7.5 earthquakes (2000–2023) with >40% NDC components. The results align well with previous studies, demonstrating robustness. This method can be extended to multiple subevents when additional constraints, such as aftershock mechanisms, are available. It offers a powerful tool for exploring complex rupture processes and understanding the physical mechanisms of large earthquakes.