NetArray, a New Seismic Array Methodology with Example Implementation for Earthquake Early Warning

ABSTRACT Accurate seismic source location remains challenging when earthquakes occur outside or near the edges of seismic networks. Standard network methods require favorable azimuthal coverage and suffer from severe distance–depth trade-offs, whereas conventional array approaches assume planar wavefronts and are restricted to distant sources. Here, we introduce NetArray, a methodology that unifies network and array approaches within a single framework. Based on a planar–radial decomposition of interstation delays, NetArray relaxes the plane-wave assumption to explicitly account for wavefront curvature. This yields a semianalytical, velocity-model-independent cost function that jointly constrains back azimuth, epicentral distance, and horizontal slowness. After the slowness vector and epicentral distance are resolved, a velocity model is used to constrain source depth, avoiding the distance–depth trade-off inherent to network methods. Synthetic tests demonstrate that NetArray notably improves back-azimuth accuracy relative to standard array methods at distances up to several times the array aperture while providing reliable estimates of epicentral distance and depth. Compared with conventional network approaches, NetArray yields more stable solutions for out-of-network sources and provides explicit minimum and maximum distance bounds for uncertainty estimation. Application to a virtual array in the Mendocino Triple Junction region highlights NetArray’s potential for earthquake early warning systems: using a limited number of stations, the method successfully mitigates the offshore distance overestimation inherited in network approaches. These results demonstrate that NetArray provides a robust, unified framework for real-time and offline seismic source location.