N. Amer C. Asia

Shading shows the smallest distance around each point that includes stations with a second azimuthal gap less than 180°. A second azimuthal gap smaller than 180° should ensure that no single arrival time controls a trade-off between origin time and epicentre. Earthquakes large enough to produce reliably measurable arrival times to these distances are most likely to have reliable epicentres computed by the ISC. All stations (blue triangles) that reported even a single phase reading are used to compute the distances.